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

Finding a decent Facebook Ads agency in London feels like trying to find a quiet pub in Soho on a Friday night. It's overwhelming, every option looks the same, and most of them will leave you with a headache and an empty wallet. The market is saturated with agencies that are brilliant at selling themselves but mediocre at actually delivering results. They talk a good game about 'brand awareness' and 'engagement' but go quiet when you ask for a clear return on ad spend.

The truth is, most founders in London pick the wrong agency. They get swayed by a slick pitch deck, impressive client logos, or a fancy office near Silicon Roundabout. They sign a 6-month contract and watch their money disappear with little to show for it. This guide is here to stop that from happening to you. We're going to give you a bulletproof framework for vetting agencies, cutting through the noise, and finding a genuine partner who can help you grow profitably.

Forget the fluff. This is about maths, methodology, and asking the tough questions that most agencies hope you won't. Let's get into it.

So, why do so many London businesses get it wrong?

The sheer number of options is the first hurdle. A quick search brings up hundreds of agencies in London, all claiming to be experts. But expertise in paid advertising, especially on a platform as competitive as Meta, is rare. It's not about being able to set up a campaign; it's about understanding the deep mechanics of the auction, the psychology of the user, and the economics of your specific business. Many agencies are generalists, offering everything from SEO to PR. While that might sound convenient, for something as specialised as paid social, you need a specialist. A jack-of-all-trades is a master of none, and in the world of paid ads, that mastery is the difference between profit and loss.

Another common mistake is focusing on vanity metrics. Agencies love to report on things like reach, impressions, and click-through rate (CTR). These numbers look good in a report but they don't pay the bills. You can have a million impressions and go out of business. The only metrics that matter are the ones tied directly to revenue and profit: Cost Per Acquisition (CPA), Return On Ad Spend (ROAS), and Lifetime Value (LTV). Any agency that doesn't lead the conversation with these metrics is either inexperienced or deliberately hiding what's important.

Finally, there's the 'big promise' trap. If an agency guarantees results, like a "guaranteed 5x ROAS," run away. Fast. No one can guarantee results in paid advertising. There are too many variables – market conditions, competitor actions, platform algorithm changes. A true expert knows this. They'll talk about a methodical testing process, realistic benchmarks, and a strategy for scaling, not about pie-in-the-sky promises. An honest conversation about potential risks is a much better sign than a confident guarantee.

The One Number You Must Know Before Hiring Anyone

Before you even think about looking at an agency's website, you need to do some homework. You need to understand the fundamental economics of your own business. The most critical number here is your Customer Lifetime Value (LTV). This tells you how much gross margin a typical customer will generate for your business over their entire relationship with you. Without this number, you're flying blind. You have no way to know how much you can afford to spend to acquire a customer (your Customer Acquisition Cost, or CAC) and still be profitable.

Calculating it is simpler than you might think. You need three pieces of data:

• -> Average Revenue Per Account (ARPA): How much revenue you get from one customer per month.
• -> Gross Margin %: Your profit margin on that revenue.
• -> Monthly Churn Rate %: The percentage of customers you lose each month.

The formula is: LTV = (ARPA * Gross Margin %) / Monthly Churn Rate

Let's take an example. Say you run a London-based subscription box service. Your box is £50 a month (ARPA). Your gross margin is 60%. And you lose about 5% of your customers each month (churn). Your LTV would be (£50 * 0.60) / 0.05 = £600. This means, on average, each customer you acquire is worth £600 in gross margin to you. A healthy business model typically aims for an LTV to CAC ratio of at least 3:1. This means you can afford to spend up to £200 to acquire that customer. Suddenly, you have a hard number to work with. When you talk to an agency, you're not just asking "Can you get us cheap clicks?". You're asking, "Can you build a system that acquires customers for under £200?". It's a completely different, and far more powerful, conversation.

To make it even easier, use this calculator to figure out your LTV and what your target CAC should be.

How to Read Case Studies (Without Being Fooled)

Armed with your LTV and target CAC, you can now start looking at agencies. Their case studies are the first port of call, but most are designed to mislead. They show off big brand logos and vague claims like "increased engagement by 200%". This tells you absolutely nothing. You need to dig deeper and look for evidence of real commercial impact.

A good case study should feel less like a marketing brochure and more like a financial report. It needs to be specific. For instance, I remember one campaign for a prize draw company where we generated £107k in revenue at a 618% ROAS. That’s specific. Another time, we took a medical job matching service's Cost Per Acquisition from £100 down to just £7. That’s a measurable business outcome. Vague claims are a huge red flag. This isn't just about finding Facebook ads experts in London; it's about finding business partners who understand numbers.

Look for relevance. If you're a B2B SaaS company, a case study about a fast-fashion eCommerce brand isn't very helpful. The strategies, audiences, and metrics are completely different. You want to see that they have experience with a business model similar to yours. It doesn't have to be the exact same niche, but if they've successfully scaled another B2B software company, for example, their experience is far more likely to be applicable to you.

Finally, the best case studies explain the 'how'. They don't just show the result; they give you a glimpse into the strategy. Did they use a specific funnel structure? Did they find success with a particular type of creative, like User-Generated Content (UGC)? Did they identify a winning audience that the client hadn't thought of? This shows they have a repeatable process, not just that they got lucky once. It's a sign of true expertise. If their case study is just a pretty picture and a big number, be sceptical.

Use this flowchart to quickly vet any case study you come across.

Turning Their Sales Pitch into Your Audition

Every agency will offer a "free consultation" or "strategy session". This is their sales process, designed to get you to sign a contract. Your job is to flip the script. This isn't a strategy session for them to give you vague advice; it's an audition for them to prove their expertise. You need to go into this meeting prepared with sharp, specific questions that test their knowledge.

Here’s what you should be asking, using the homework you've already done:

1. "Based on my LTV of £X and my price point, what would you consider a realistic target CPA for us in the UK market on Meta?" This question immediately grounds the conversation in profitability. A good answer won't be a single number. It will be a range, and they should be able to justify it based on their experience with similar clients and current auction costs. I recall one client, an HVAC company in a competitive area, seeing costs around $60 per lead. For others, like a home cleaning service we worked with, we achieved a £5 CPL. The answer should show they understand the nuances of the market.


2. "What is your testing methodology for creative and audiences?" This probes their process. A weak answer is "we test lots of things". A strong answer is "We start with 3 distinct audience hypotheses and 3 creative concepts based on a Problem-Agitate-Solve framework. We'd allocate a small budget to test these in an ABO campaign to find initial winners, then move winning assets into a CBO campaign for scaling." This shows they have a structured, methodical approach.


3. "Who will actually be working on my account, and can I speak to them?" Many London agencies use a classic bait-and-switch. You get sold by the charismatic founder or senior strategist, but then your account is handed off to a junior account manager with six months of experience. You need to know who is responsible for the day-to-day management and what their level of experience is. Insist on having the actual account manager on the call. It's a massive red flag if they refuse.


4. "Can you walk me through an example of an ad account structure you would build for a business like ours?" This is a technical question that separates the real practitioners from the salespeople. They should be able to sketch out a logical campaign structure, likely involving top-of-funnel prospecting campaigns (ToFu), middle-of-funnel retargeting (MoFu), and bottom-of-funnel conversion campaigns (BoFu). If they can't answer this clearly and confidently, they don't have the hands-on expertise you need.

Their answers to these questions will tell you everything you need to know. Are they talking in specifics or generalities? Are they focused on your business outcomes or their agency process? Do they sound like a strategic partner or a glorified button-pusher? A great Meta ads expert in the UK will welcome these questions because it gives them a chance to demonstrate their depth of knowledge. A weak agency will get flustered.

What Does a Good Meta Strategy for London Look Like Anyway?

The London and UK market is one of the most competitive in the world. This means higher costs and more sophisticated consumers who are tired of bad advertising. A generic strategy that works in other markets will likely fail here. A competent agency should be talking about a strategy that reflects this reality.

Audience Targeting is Nuanced: The agency should have a clear plan for audience prioritisation. For a new account, they should start with detailed targeting (interests, behaviours) to gather data. As the pixel seasons, they should be layering in lookalike audiences built from high-intent actions (like purchasers or checkout initiators) and sophisticated retargeting segments. It's not just about retargeting all website visitors; it's about segmenting users based on their behaviour and showing them tailored messaging. For example, someone who abandoned their cart needs a different message to someone who just read a blog post.

Creative is the Biggest Lever: In a crowded market, the creative is your single biggest advantage. The agency should have a robust plan for creative testing. This means testing different formats (video, image, carousel), different hooks, and different messaging angles. They should be talking about things like UGC, which performs incredibly well in the UK right now, and how they would go about sourcing or producing it. If their creative strategy is just "you give us the images and we'll write some copy", that's not good enough.

The Funnel is Everything: A good strategy recognises that not everyone is ready to buy right away. It should map to a proper marketing funnel.

• ToFu (Top of Funnel): Prospecting campaigns to reach new audiences who've never heard of you. The goal here isn't necessarily immediate sales but to build awareness and drive traffic.
• MoFu (Middle of Funnel): Engaging people who have shown some interest (e.g., watched a video, visited your site). This could involve retargeting them with case studies, testimonials, or different product benefits.
• BoFu (Bottom of Funnel): This is where you go for the kill. Targeting people who have shown strong buying signals (e.g., added to cart, initiated checkout) with direct offers and reminders to complete their purchase.

An agency that just sets up a single conversion campaign and hopes for the best doesn't understand modern paid social. They need a full-funnel approach.

Your Final Vetting Checklist

Choosing an agency is a big decision. It’s a significant investment of both money and trust. To make it as objective as possible, you need a structured way to compare your options. After you've spoken to a few shortlisted agencies, use the table below to score them. This isn't about finding an agency that scores a perfect 10/10 on everything; it's about finding the one with the best overall fit for your business, with strengths in the areas that matter most to you. There's a lot to consider, from their technical skills to how they manage costs, which is why a comprehensive guide on Facebook ads management costs can be a useful companion to this checklist.

Be honest in your assessment. Did they truly understand your business, or did they just deliver a generic pitch? Were their answers to your tough questions confident and specific, or did they hedge and deflect? This process forces you to move beyond a gut feeling and make a data-informed decision. Don't rush it. The time you invest now in proper due diligence will pay for itself many times over in the long run.

So, what now?

Choosing the right partner to manage your paid advertising is one of the most important decisions you'll make for your business's growth. The right agency can be a powerful engine for predictable, profitable scaling. The wrong one can burn through your cash, waste your time, and leave you feeling cynical about advertising altogether. As you've seen, the process of finding a great one, especially in a competitive hub like London, requires a methodical approach. It requires you to be informed, ask tough questions, and focus relentlessly on the numbers that actually matter.

This process of due diligence—calculating your LTV, dissecting case studies, and turning consultations into auditions—is not easy. It takes time and a level of expertise you might not have in-house. That’s perfectly okay. Recognising when you need specialist help is the mark of a smart founder. If you've read this guide and feel that navigating this process alone is a daunting task, then it might be time to speak with experts who live and breathe this stuff every single day.

We offer a completely free, no-obligation strategy session where we can help you with this. We won't give you a hard sales pitch. We'll simply review your current situation, help you understand your key metrics, and give you honest, actionable advice on what your next steps should be. It's a chance for you to experience our expertise firsthand and see if we're the right fit to help you achieve your growth goals. If you're ready to stop guessing and start building a truly effective advertising strategy, feel free to get in touch.