London's Facebook Ads Experts: The Founder's Vetting Guide

I get it. You're based in London, you need to grow, and you're drowning in a sea of "award-winning" Meta Ads agencies all promising the earth. They've all got slick offices in Shoreditch or Canary Wharf, sharp-suited sales guys, and a portfolio that looks suspiciously generic. The problem is, 90% of them are terrible. They are brilliant at selling retainers, but shockingly bad at delivering results.

They'll take your money, assign your account to a junior exec who's juggling 20 other clients, run some basic interest-targeting campaigns, and send you a pretty report full of vanity metrics like 'reach' and 'impressions' while your bank account quietly shrinks. Choosing the right agency isn't about finding the one with the best sales pitch; it's about having a rigorous vetting process to filter out the charlatans and find a true partner. This is that process.

So, why will most London agencies burn your cash?

Let's be brutally honest. The typical agency model is fundamentally broken, especially in a high-cost city like London. The economics demand a constant flow of new clients to cover the enormous overheads. This creates a machine optimised for sales, not for client success. The partner or director who sells you the dream on the intro call is almost never the person who will actually be in your ad account building campaigns. That job falls to an overworked, under-experienced account manager who is following a template.

Their goal isn't to deeply understand your customer's pain points and craft a bespoke strategy. Their goal is to get your campaigns live as quickly as possible, hit a few surface-level KPIs so the monthly report looks okay, and move on to the next fire. They'll talk about "best practices" which is agency-speak for "the same thing we do for everyone else." For a business that needs real, profitable growth, this is a death sentence. You're not paying for expertise; you're paying for access to a button-pusher.

A huge red flag is any agency that promises or "guarantees" results. In paid advertising, nothing is guaranteed. Tbh in paid advertising, you can't really promise anything as it's impossible to predict how exactly the ads will perform. Market conditions change, ad platforms update their algorithms, creative fatigues. A real expert knows this. They don't promise results; they promise a rigorous, data-driven process of testing and optimisation to find what works. If it sounds too good to be true, it's because it is. They're telling you what you want to hear to get the contract signed. This is why you need to shift the conversation away from their promises and onto your numbers.

What's the one metric they should be asking you about?

If an agency starts the conversation by talking about ROAS (Return On Ad Spend), be wary. It’s not that ROAS is useless, but out of context, it’s a vanity metric. A 10x ROAS is terrible if your profit margin is 5%. A 2x ROAS can be fantastic if your margin is 80% and you have a high repeat purchase rate. A great agency knows this. They won't talk about ROAS; they'll ask about your unit economics.

The real question isn't "How low can my Cost Per Lead go?" but "How high a CPL can I afford to acquire a truly great customer?" The answer lies in its counterpart: Lifetime Value (LTV). This is the foundation of any succesful paid advertising campaign.

Here’s the simple maths. You need to know these numbers for your own business, and any agency worth their salt will force you to confront them:

• Average Revenue Per Account (ARPA): What do you make per customer, per month/year?
• Gross Margin %: What's your profit margin on that revenue after cost of goods sold?
• Monthly Churn Rate: What percentage of customers do you lose each month?

The calculation is straightforward:

LTV = (ARPA * Gross Margin %) / Monthly Churn Rate

For example, if your ARPA is £200, your gross margin is 70%, and you lose 5% of your customers each month, your LTV is (£200 * 0.70) / 0.05 = £2,800. Each customer is worth £2,800 in gross margin to your business over their lifetime.

This single number changes everything. A healthy business model aims for at least a 3:1 LTV to CAC (Customer Acquisition Cost) ratio. In our example, with a £2,800 LTV, you can afford to spend up to £933 to acquire a single customer and still have a very healthy business. Suddenly that £100 CPL from Meta ads doesn’t seem so scary, does it?

This is the language of growth. A top-tier agency partner thinks like an investor in your business. They want to know these numbers so they can set realistic targets and build a strategy that is profitable from day one. An agency that doesn't ask about this is just planning to spend your money. Use the calculator below to get a clear picture of your own LTV. If you don't know these numbers, your first job is to figure them out before you spend a single extra pound on ads.

How to properly interrogate their case studies

Once you've established your numbers, the next step is to see if the agency has a track record of delivering profitable growth for businesses like yours. Every agency website has a "Case Studies" or "Results" page. Most of them are useless, filled with vanity metrics and impressive-sounding claims with no substance. Your job is to become a forensic accountant and pick them apart.

Take a good look at their case studies. See whether they have experience with a similar niche and whether they were able to drive results for these clients. Of course, you gotta be realistic results wise as it might be difficult or competitive in your niche. But if they've got good case studies and it sounds like they truly have the expertise, that's a great sign. We have detailed case studies walking through the full strategies and results we've implemented for clients that give any prospective client a really good idea what we can do for them.

Don't be impressed by big logos. A massive brand can get results with mediocre advertising just due to brand recognition. Look for case studies from businesses that look like yours – similar size, similar industry, similar challenges. Here in London, that might mean looking for specific experience in FinTech, B2B SaaS, or high-end D2C eCommerce, rather than generic retail. Look for results in pounds (£), not just dollars.

A great case study doesn't just show the result; it tells the story of the problem, the strategy, and the process. It should talk about the challenges they faced and how they overcame them. For instance, I remember one campaign for a SaaS client in the medical recruitment space where the initial CPA was over £100. A good case study wouldn't just state the final result. It would explain the process of how we managed to bring that CPA down to just £7 using both Google and Meta Ads. That's a story of expertise, not just a lucky result.

Use the flowchart below as a mental model when you're reviewing a case study. If you can't answer "Yes" to these questions, the case study is probably marketing fluff.

The 'Free Consultation' is your interrogation room

Every agency offers a "free consultation," "strategy session," or "account audit." You need to reframe this in your mind. This is not a gift from them to you. This is your single best opportunity to interview them and expose their weaknesses. Their sales team has a script. Your job is to break that script with questions they can't answer with pre-prepared platitudes.

Get on a call with them, book in an intro meeting and ask away, see what advice they have for you. Look for expertise here, like they know what they are doing and aren't just promising you results. This is the core of our recommended founder's vetting framework for London agencies.

Don't let them control the conversation. Come prepared with a list of sharp, specific questions. Here are a few to get you started:

• "Walk me through a campaign you ran that failed. What did you learn and how did you pivot?" This is the most important question you can ask. A good agency isn't one that never fails; it's one that learns and adapts quickly when things don't work. If they can't answer this, they're either lying or inexperienced. Their answer will reveal their problem-solving process and their honesty.


• "Based on the LTV I shared, what would you consider a sustainable CAC for us, and how long do you estimate it will take to get there?" This question immediately tests if they were listening and if they think in terms of business metrics. A vague answer like "we'll aim for the lowest possible CAC" is a red flag. A good answer will be a thoughtful range, with clear assumptions laid out, like "Given your £2,800 LTV, we should aim for a CAC under £900. In the first month, we might see a higher CAC of around £1200 as we test audiences, but we'd expect to bring that down into the target range by month three."


• "Who, specifically, will be working on my account day-to-day? Can I speak with them? What's their direct experience with [your industry]?" This cuts through the classic bait-and-switch where a senior director sells you, but a junior graduate runs your account. You're paying for expertise. You have every right to know exactly who you're getting. If they're hesitant to let you speak to the actual practitioner, it's a massive red flag.


• "Your case study for [Client X] is impressive. What was the total ad spend for that campaign to achieve those results, and over what period?" This adds crucial context to their shiny results. A £100k revenue result is amazing on £10k ad spend (10x ROAS), but it's a disaster on £200k ad spend (0.5x ROAS). This forces them to be transparent about the economics behind their success stories.


• "What's your process for creative testing? How do you develop ad copy and creative, and how often do you refresh it?" Many agencies are lazy with creative. They'll ask you for a few images and write some basic copy, then run it into the ground. A great agency has a rigorous process. They'll talk about testing different angles, hooks, and formats (video, image, carousel). They might even have copywriters or designers in-house or work with trusted partners. Their process for creative is often a direct reflection of the quality of their service.


• "Beyond optimising the ads, what are your initial thoughts on our landing page and offer? What would you change?" This is a killer question. A button-pusher agency will say "the page looks fine, let's just send traffic." A true growth partner will immediately start critiquing your offer. They'll point out a lack of social proof, a confusing call to action, or a weak headline. They know that the best ads in the world can't save a bad landing page. An agency that isn't afraid to challenge you on your own website is one that is genuinely invested in your success.

Their answers to these questions will tell you everything you need to know. You're looking for depth, transparency, and a focus on business fundamentals, not just ad platform tactics. Many agencies won't have good answers. That's a good thing. It means your filter is working.

Decoding the murky world of London ad agency pricing

Once you're confident in an agency's expertise, the final piece of the puzzle is their pricing. Agency fees in London can feel all over the place, and the model they use can create very different incentives. Understanding these models is critical to forging a healthy partnership. It's a topic we've covered in detail in our guide to London ad agency pricing, but here's a quick breakdown.

There are three common models you'll encounter:

1. Percentage of Ad Spend: This is the most common. The agency takes a cut of whatever you spend on ads, typically between 10-20%. It's simple to understand, but it has a fundamental flaw: the agency is incentivised to make you spend more, even if it's not profitable. This can work if you have a high degree of trust, but it's a conflict of interest you need to be aware of.


2. Flat Monthly Retainer: You pay a fixed fee each month, regardless of ad spend. This is predictable for your budgeting and aligns your interests better – the agency's goal is to make the fixed fee worth it by delivering great results. The downside is that it can lead to complacency if there aren't clear performance indicators tied to the retainer. The cost for a Facebook ads manager in London can range from £1,500 to over £10,000 per month, depending on the scope and expertise.


3. Performance-Based: This sounds like the holy grail – you only pay for results (e.g., per lead, or a percentage of revenue generated). While attractive, the devil is always in the detail. These agreements can be complex, with tricky definitions of what constitutes a "lead" and attribution challenges. It's rare to find a reputable agency offering a purely performance-based model for new clients, as they're taking on all the risk of your offer and website not converting.

Often, you'll see hybrid models, like a lower flat retainer plus a smaller performance bonus. This can be a good compromise, aligning incentives while providing the agency with some stability. Whichever model you consider, the key is to understand how it incentivises the agency and ensure it aligns with your goals.

Final check: Red flags that should make you run

You've done your homework. You know your numbers, you've interrogated their case studies, you've grilled them in the consultation, and you understand their pricing. Before you sign on the dotted line, run through this final checklist of red flags. If you spot any of these, think very carefully before proceeding.

• Long-term contracts from the start. A confident agency doesn't need to lock you into a 12-month contract. They'll be happy to start with a 3-month trial or a rolling monthly agreement because they're confident they can prove their value. A long contract is a sign they're worried you'll want to leave once you see the actual results.


• Vague, fluffy reporting. If their sample reports are full of screenshots of the Facebook Ads manager focusing on impressions, reach, and clicks, it's a bad sign. You want a report that speaks your language: leads, cost per lead, customers, revenue, CAC, and LTV. It should clearly explain what they tested, what they learned, and what the plan is for next month.


• Lack of direct access to the practitioner. If you're only ever allowed to speak to a client-facing account manager who acts as a middleman, you'll lose crucial context and speed. You should have a direct line (like a shared Slack channel) to the person who is actually in your account building campaigns.


• Requesting references after the fact. This is a contrarian one, but it's important. Tbh if someone asks us for references or to call one of our clients after they've already reviewed our case studies and gotten a free, in-depth account review, it's an instant red flag *for us*. It signals a fundamental lack of trust that no amount of proof will satisfy. A good partnership is built on trust from the beginning. Do your research up front – look at their reviews, case studies, and the value they provide in the consultation. If you're still not convinced, you probably shouldn't work with them, and they probably shouldn't work with you.

Finding the right agency is hard work. But the alternative – partnering with the wrong one – is far more expensive. It doesn't just cost you the agency fee; it costs you months of lost opportunity and wasted ad spend. By following this framework, you can cut through the noise and find a genuine growth partner who can help you scale profitably.

This is the main advice I have for you:

I've detailed the main recommendations for you below. This isn't just a checklist; it's a strategic framework for making one of the most important marketing decisions for your business.

Ultimately, choosing an agency is choosing a partner. You're not just buying a service; you're bringing an external team into the core of your business's growth engine. The process should be rigorous and deliberate. It requires more work from you upfront, but it dramatically increases your chances of finding a partner who will deliver real, measurable results and become an invaluable asset to your company.

If you've been through this process and are looking for a no-nonsense, results-focused partner to scale your Meta ads, we offer a completely free, no-obligation strategy session where we'll audit your existing campaigns and give you actionable advice you can implement immediately. Feel free to get in touch to see if we're a good fit.