The UK Startup's Guide To Vetting Paid Ad Agencies

Finding a good paid ads agency as a UK startup is a proper nightmare. The market is saturated with outfits that talk a good game, flash some fancy client logos, and then stick a junior account manager on your business who burns through your seed funding faster than you can say "vanity metrics". They sell you a dream based on a slick sales pitch, lock you into a long contract, and deliver nothing but disappointment. I've seen it countless times.

The problem is, most founders don't know how to properly vet an agency. They ask the wrong questions, look for the wrong things, and get swayed by promises that have no basis in reality. This guide is here to fix that. I'm going to give you a brutally honest, no-nonsense framework for finding a partner who can actually move the needle for your business, not just drain your bank account.

So, why is it so bloody hard to find the right agency?

First off, most agencies are generalists. They'll run ads for a local plumber one day and a global SaaS company the next. They might understand the mechanics of Google Ads or Meta Ads, but they don't understand the specific pressures of a startup. They don't think in terms of CAC payback periods, LTV, monthly burn rates, or the urgent need to show traction to your investors. They're used to big, slow-moving corporate clients with massive brand awareness budgets. For them, "brand awareness" is a legitimate campaign goal. For a startup, it's a death sentence. You need conversions, you need them now, and you need to acquire them profitably.

The London agency scene is particularly tricky. It's full of big names, shiny offices in Shoreditch, and impressive-looking awards. But often, that's all for show. You get pitched by a senior partner who seems to know their stuff, but the moment you sign the contract, your account is handed off to someone with maybe a year or two of experince. You're paying for the senior partner's expertise, but you're getting the work of a novice. It's a classic bait-and-switch.

Another common mistake is thinking you need a local agency. I hear it all the time: "I want someone I can meet for a coffee in Manchester" or "I need an agency based in London". Honestly, location is one of the least important factors. In today's world, it's completely irrelevant. What matters is expertise. Would you rather have a mediocre agency down the road, or a world-class specialist team on the other side of the country (or even the world) that has a proven track record of scaling businesses exactly like yours? I remember one SaaS client we worked with, a medical job matching platform. They came to us after working with a big, well-known London agency that had got their CPA to around £100. We took it over and, by applying our specialist SaaS scaling methodology, got their CPA down to just £7. We never met them in person. The results spoke for themselves.

You have to understand that not all agencies are created equal. You have large network agencies, boutique specialists, solo consultants, and everything in between. For a startup, you almost always want a specialist. Someone who lives and breathes your world, whether that's B2B SaaS, D2C eCommerce, or high-ticket courses. A generalist can't give you the strategic depth you need.

What should I actually be looking for then?

This is where you need to change your mindset from a client hiring a vendor to an investor doing due diligence. Your marketing budget is an investment, and you need to be damn sure the people managing it are going to give you a return.

Drill into their Case Studies. No, really drill in.
This is your number one priority. Don't just glance at the logos on their website. Ask for detailed case studies. And when you read them, look for these things:

-> Relevance: Have they worked with companies at a similar stage to you? With a similar business model? In a similar (or adjacent) niche? Getting results for a massive brand like Nike is completely different from getting results for a seed-stage SaaS startup. I remember for one software client, we generated 5,082 trials from Meta Ads, and for another B2B SaaS business, we drove 1,535 trials. That's the kind of specific, relevant result you want to see if you're a SaaS founder.

-> Real Metrics: The case study should talk about business metrics, not ad metrics. I don't care about a 200% increase in click-through rate. I care about revenue, ROAS (Return on Ad Spend), CPA (Cost Per Acquisition), and lead-to-customer conversion rates. If their case studies are full of fluff like "impressions" and "reach," run away. One of our eCommerce campaigns for a cleaning products company generated a 633% return and a 190% increase in revenue. That's a business result.

-> The 'How': A good case study should give you some insight into their strategic thinking. What was the problem? What was their hypothesis? What did they test? What was the outcome? It shouldn't just say "we ran some Facebook ads and they did great." It should give you a glimpse into their process.

You can see from a company's case studies wether they have the expertise you're looking for. If they sound like they know what they are talking about, that's a great sign. But if it feels like they don't have the expertise you need, after you've looked through their case studies, then it's probably not a good fit. Tbh, if a potential client asks us for references or to call one of our current clients after they've already reviewed our case studies and had a free, in-depth strategy session with us, it's an instant red flag. It shows a fundamental lack of trust from the start, and that's not a foundation for a good partnership.

The First Call is a Two-Way Street
Most founders go into an initial call with an agency ready to be sold to. Big mistake. You should be interviewing them just as much as they're qualifying you. Here are the questions you should be asking, and the answers you should be looking for:

-> "What's your process for onboarding a new client like me?"
A good answer will involve a deep dive into your business, your customers, your offer, your economics (LTV, margins), and your goals. A bad answer is "You give us your credit card and access to your ad account, and we'll start running ads."

-> "Based on what you know so far, what do you see as my biggest challenge and my biggest opportunity?"
This tests their strategic thinking. Can they diagnose a problem quickly? Do they see beyond just "running ads"? A great agency might say, "Your biggest challenge isn't your ads, it's your offer. A 'Request a Demo' CTA has too much friction for cold traffic. We should test a high-value content offer first to build trust." That's a partner, not a pixel-pusher.

-> "Who will actually be working on my account?"
Get clarity on this. Will it be the senior person you're talking to, or a junior account manager? Ask about the experience of the person who'll be in the weeds of your account day-to-day.

We offer a free initial consultation where we review a prospect's strategy and ad account together. It's incredibly valuable for them because they walk away with actionable advice, and it gives them a real taste of the expertise they'd be getting if they work with us. Look for an agency that's willing to give you value upfront, before you've paid them a single penny. It shows confidence in their ability to deliver.

Are they just good at sales, or do they have real expertise?

This is the crux of it. A slick salesperson can promise you the world, but it's the strategist in the background who delivers it. Real expertise isn't about knowing which buttons to press in the Facebook Ads Manager. It's about understanding business strategy and human psychology.

A true expert will challenge you. They'll question your assumptions about your target audience. They'll tell you your landing page isn't good enough. They might even tell you that you're not ready for paid ads yet. This might sound harsh, but it's what you're paying for. You don't want a "yes-man" who will happily take your money and run ads to a broken funnel. You want a partner who will tell you the hard truths because they are invested in your success.

The biggest giveaway is whether they talk about your offer. In my experience, the number one reason campaigns fail is a weak offer. A brilliant ad campaign pointing to a mediocre offer will always fail. A mediocre ad campaign pointing to an irresistible offer can still succeed. An agency that doesn't spend a significant amount of time discussing, critiquing, and helping you refine your offer isn't an expert agency. They are a media buying service.

For example, so many B2B founders are obsessed with the "Request a Demo" button. It's the most arrogant Call to Action in marketing. It assumes your prospect has nothing better to do than get on a call to be sold to. It's high-friction and low-value. A real expert would push you to create a better offer. For a SaaS business, that's a free trial or a freemium plan. Let the product do the selling. For a service business, it could be a free audit, a valuable template, or an insightful guide. You must solve a small problem for free to earn the right to solve the big one. An agency that understands this is worth its weight in gold.

They should also be obsessed with your customer's pain. They should be trying to get inside their head. Forget demographics like "males aged 25-40". That's useless. You need to define your customer by their nightmare. What's the urgent, expensive, career-threatening problem that keeps them up at night? An agency that helps you articulate this is thinking on a completely different level. They're not just targeting an audience; they're crafting a message that resonates deeply with a specific problem state, which is infinitely more powerful.

How much can I realy afford to spend? Hint: It depends on your LTV.

Before you even think about agency fees or ad spend, you need to know your numbers. The most important number is your Customer Lifetime Value (LTV). This single metric dictates your entire growth strategy. The question isn't "how low can I get my cost per lead?", but "how high a cost per lead can I afford to acquire a fantastic customer?"

Most founders either don't know their LTV or calculate it wrong. Here’s a simple way to get a solid estimate:

Average Revenue Per Account (ARPA): What's the average amount a customer pays you each month?
Gross Margin %: What's your profit margin on that revenue?
Monthly Churn Rate: What percentage of customers cancel each month?

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

Let's say you run a SaaS business. Your average customer pays you £200/month (ARPA), your gross margin is 80%, and you lose 5% of your customers each month (churn).

LTV = (£200 * 0.80) / 0.05
LTV = £160 / 0.05 = £3,200

This means, on average, each customer you acquire is worth £3,200 in gross margin over their lifetime. Now you have your North Star. A healthy LTV to CAC (Customer Acquisition Cost) ratio is generally considered to be 3:1. This means you can afford to spend up to £1,066 (£3,200 / 3) to acquire a single new customer. If your sales team converts 1 in 5 qualified leads into a customer, you can afford to pay up to £213 per qualified lead. Suddenly that £100 lead from Google Ads doesn't seem so expensive, does it?

Use this calculator below to get a feel for your own numbers. This is the maths that unlocks aggressive, intelligent scaling. An agency that doesn't ask you for these numbers in the first call is flying blind.

As for agency fees in the UK, they vary wildly. But for a startup, you're typically looking at a few models:
-> Flat Retainer: A fixed fee each month. This is common and can range from £1,500 to £10,000+ per month, depending on the agency's reputation and the scope of work. It's predictable, which is good for budgeting.
-> Percentage of Ad Spend: Usually 10-20% of your monthly ad spend. This model incentivises the agency to get you to spend more, which isn't always aligned with your goal of profitability. Be wary of this one at the early stages.
-> Performance-Based: A lower retainer plus a bonus based on hitting certain targets (e.g., a fee per lead or a percentage of revenue generated). This can be great as it aligns incentives, but the targets need to be set carefully and realistically.

Don't just go for the cheapest option. As the old saying goes, if you think a professional is expensive, wait until you hire an amateur. The cost of a bad agency isn't just their fee; it's the wasted ad spend and the months of lost opportunity you can never get back. Instead, consider this part of your overall marketing investment and find the right UK paid ads agency that can deliver a return.

What are the biggest red flags to run away from?

I've hinted at some of these already, but let's put them all in one place. If you see any of these during your vetting process, you should think very carefully before proceeding. It's much easier to avoid a bad partnership than to get out of one.

Ultimately, choosing an agency is one of the most important decisions you'll make as a founder. It's not just a line item on your P&L; it's a partnership that can make or break your growth trajectory. Too many startups get this wrong and pay a heavy price. They either hire the wrong agency and burn through cash, or they get scared and try to do it all themselves, making costly mistakes along the way. Deciding between DIY vs hiring an agency is a critical step, and if you choose the agency route, you need to do it right.

The right partner will feel less like an external supplier and more like an extension of your own team. They'll be as obsessed with your numbers as you are, they'll bring new ideas to the table, and they'll hold you accountable just as you hold them accountable. This guide isn't just about hiring an agency; it's about finding that strategic growth partner. If you're a founder in London, for instance, there's a specific method for vetting the local agencies to separate the substance from the hype.

The Final Decision

After you've done your research, reviewed the case studies, and had the initial calls, you should have a clear frontrunner. The final step is to review their proposal and contract in detail. The proposal shouldn't be a copy-paste job. It should reflect the conversations you've had and outline a clear, customised plan for the first 90 days. It should set realistic goals and define what success looks like for both parties.

Don't be afraid to negotiate. If you're not comfortable with a 6-month contract, ask for a 3-month trial period. If the reporting structure isn't clear, ask for it to be defined. A good agency will be happy to work with you to create a partnership that feels fair and transparent.

This whole process takes time and effort, but it's worth it. The difference between the right agency and the wrong agency can be the difference between stagnating and achieving explosive growth.

I've detailed my main recommendations for you below:

If you go through this process, you'll be in a much stronger position to find a genuine growth partner. It requires more work upfront, but it will save you a huge amount of money, time, and stress in the long run. The right agency can be a powerful catalyst for your startup's success, but only if you choose wisely.

If you're a founder who is tired of the agency runaround and wants a no-nonsense, results-focused approach, you might benefit from some expert help. We offer a free, 20-minute strategy session where we'll audit your current advertising efforts (or lack thereof) and give you a clear, actionable plan. There's no sales pitch, just straightforward advice from specialists who have been in the trenches scaling startups like yours. Feel free to schedule a call.