SaaS Paid Ads: UK Founder's Guide To Agency Vetting

I get it. You're a UK SaaS founder, you've got a great product, but you're struggling to get traction with paid ads. So you start looking for an agency. You're immediately hit with a wall of jargon, promises of "sky-high ROI," and dozens of agencies that claim to be "data-driven experts." The problem is, most of them have never scaled a SaaS business past the free trial stage in their life. They're generalists who think running ads for a local plumber is the same as acquiring users for a complex B2B software product. It's not.

Tbh, finding the right agency is one of the most difficult parts of scaling. Get it wrong, and you'll burn through your seed funding with nothing to show for it but a dashboard full of useless clicks. Get it right, and it's like pouring petrol on a fire. This guide is my attempt to give you a proper framework for making that decision, based on years of being on the other side of the table and seeing where founders go wrong. We're going to skip the fluff and get straight to what actually works.

So, why do so many founders hire the wrong agency?

It usually comes down to a few common mistakes. The first is getting obsessed with location. I've spoken to dozens of founders in Manchester, Bristol, and Edinburgh who are adamant they need an agency down the road. Why? So you can have a coffee once a quarter? In 2024? The best talent for your specific SaaS niche might be in London, or they might be in Leeds. It doesn't matter. What matters is their expertise in your world. Focussing on finding a B2B ad agency in London just because it's the capital is a rookie mistake; focus on expertise over postcode.

The second trap is the "full-service" agency. They offer SEO, content, social media management, email marketing, and paid ads. It sounds great, but in reality, they're a jack of all trades and a master of none. SaaS paid acquisition is a specialism. It requires a deep understanding of platforms like LinkedIn and Google Search for high-intent users, and knowing how to make Meta work for what can be a very specific B2B audience. I remember one campaign we worked on for a B2B software client generated 4,622 registrations at just $2.38 each on Meta—that result didn't come from a generalist's playbook.

Finally, founders get seduced by vanity metrics. An agency shows you a chart with impressions going up and to the right. Looks impressive, doesn't it? But impressions don't pay the bills. Clicks don't pay the bills. You need sign-ups, trials, demos, and ultimately, paying customers. If an agency isn't talking about Cost Per Acquisition (CPA), trial-to-paid conversion rates, and LTV:CAC ratios from day one, they're not the right partner for a subscription business. They're just selling you expensive traffic.

How to spot real SaaS expertise

So, how do you find an agency that actually knows what they're doing in the SaaS world? You need to look for verifiable proof. It's that simple. And that proof comes in the form of detailed case studies.

I don't mean a page with a bunch of logos on it. I mean a proper walkthrough of a campaign for a business like yours. It should detail the initial problem, the strategy they implemented, the platforms they used, and the results they achieved. And those results need to be in numbers that matter to a SaaS founder. I'm talking about things like:

• -> How we got 5,082 software trials at a $7 cost per trial on Meta Ads.
• -> How we reduced a £100 Cost Per User Acquisition down to just £7 for a medical job matching SaaS.
• -> How we generated 1,535 trials for a B2B SaaS platform using Meta.

These are real results from campaigns we've run. They're specific and they speak the language of SaaS growth. If an agency's case studies talk about "brand uplift" or "increased engagement," they're not for you. You need an agency that measures success in new MRR, not likes and shares. You might find our ultimate guide to vetting a SaaS agency in London helpful for more specific questions to ask.

Beyond case studies, listen to the language they use on a discovery call. Do they understand the difference between a Marketing Qualified Lead (MQL) and a Product Qualified Lead (PQL)? Do they ask about your churn rate and average revenue per user (ARPU)? Do they immediately start talking about building seperate campaigns for top-of-funnel, middle-of-funnel, and bottom-of-funnel audiences? If they don't, it's a sign they're applying a generic B2C eCommerce model to your highly specific SaaS business. This is especially true for more complex platforms; for example, if you're looking to advertise on LinkedIn, you really need someone who understands the nuances, which is why we put together an entire guide on running LinkedIn ads for UK SaaS lead generation.

The Vetting Process: A Founder's Interrogation Checklist

Once you've got a shortlist of agencies that seem to have the right specialism, it's time to put them to the test. This isn't a sales call where you sit back and listen to their pitch. This is an interview. You are the one in control. Your goal is to get past the sales fluff and understand how they actually think and operate.

Step 1: The Website Recon
Before you even speak to them, do a deep dive on their website. Is it professional? Is the copy clear and persuasive? If they can't market themselves effectively, how can you trust them to market you? Look for those detailed case studies we talked about. Look for articles or guides that demonstrate their expertise. Do they have a clear point of view or is it just generic marketing waffle? The quality of their own content is a massive clue.

Step 2: The Discovery Call Interrogation
When you get them on a call, have your questions ready. Here are a few of my favourites to seperate the experts from the amateurs:

• "Walk me through a SaaS campaign you ran that failed at first. What went wrong and what did you do to fix it?" This is the most important question you can ask. Anyone can talk about their wins. True experts are honest about their failures because that's where the real learning happens. If they claim they've never had a campaign fail, they're either lying or they're inexperienced. You're listening for a structured, analytical response about testing, iterating, and problem-solving.
• "What's your process for understanding our Ideal Customer Profile (ICP) and their pain points?" A weak answer is "we'll look at your current customers." A strong answer will involve them conducting their own research, analysing your competitors, and building detailed personas based on "nightmare scenarios"—the specific, urgent problems your software solves.
• "Beyond CPL/CPA, how will you help us measure the down-funnel success of your campaigns? How will you track trial-to-paid conversion rates?" This tests their understanding of SaaS business models. The right agency will talk about integrating with your CRM, using tracking parameters, and building dashboards that connect ad spend to actual revenue, not just top-level leads.
• "Who, specifically, will be working on our account day-to-day? Can I speak with them?" Often, you'll get sold by the senior, charismatic director, but your account will be handed off to a junior who is learning on your dime. Insist on knowing who is actually managing your money and what their direct experience with SaaS is. This whole question of who to hire is complex, and it's worth considering whether you need a full SaaS marketing consultant or an agency.

Step 3: The "Free Audit" Litmus Test
Many agencies, including us, offer a free audit or strategy session. This is your single best opportunity to see them in action. Tbh, if an agency isn't willing to offer this, I'd be very skeptical. It shows a lack of confidence in their own ability to provide value upfront.

During this session, don't let them just give you a generic presentation. They should have looked at your website, your current ads (if you're running any), and your competitors. They should come to the meeting with specific, actionable insights. A good session will leave you with at least one "aha!" moment and a few things you could go and implement yourself immediately. A bad session will feel like a veiled sales pitch where they tell you everything is broken and only they can fix it. Use this as the final test. If they can't impress you with their thinking for 30 minutes, they definately won't impress you over a 6-month contract.

What's a realistic ROI? Understanding the numbers that matter

Okay, let's talk about the big one: Return on Investment. Every agency promises it, but few can actually deliver it in a predictable way for SaaS. The key is to stop thinking about immediate return and start thinking about Lifetime Value (LTV). You're not selling a £50 pair of trainers; you're acquiring a customer who might pay you hundreds or thousands of pounds over several years.

This is where most founders and many agencies get it wrong. They obsess over getting the Cost Per Lead (CPL) as low as possible. But a cheap lead that never converts to a paying customer is worthless. I'd rather pay £250 for a qualified demo request from a CTO that turns into a £10,000/year contract than £5 for a lead from a student who just wanted to download a whitepaper.

The first thing you need to do, before you even think about ROI, is calculate your LTV. It's the most powerful number in your business. Here's a simplified way to do it:

LTV = (Average Revenue Per Account [ARPA] * Gross Margin %) / Monthly Churn Rate

Once you know what a customer is worth to you, you can work backwards to figure out what you can afford to spend to acquire them (your Customer Acquisition Cost, or CAC). A healthy LTV:CAC ratio for a growing SaaS business is typically at least 3:1. This means for every £1 you spend on acquiring a customer, you should get at least £3 back in lifetime gross margin. Knowing this number completely changes the conversation about ad performance. If your LTV is £5,000, a £500 CPA might be an incredible bargain. Without knowing your LTV, you're flying blind. For a more detailed breakdown, you might want to look at our complete UK B2B agency ROI guide.

Reading the proposal and spotting the red flags

You've done your due diligence, you've interrogated the candidates, and you've found an agency you think is a good fit. They send over the proposal. This is the final hurdle. How you read this document can save you a lot of headaches down the line.

A good proposal won't be a generic, copy-pasted document. It will be tailored to your business and the conversation you had. It should clearly outline:

• The Strategy: A summary of their initial strategic thinking. Which platforms they recommend and why. What initial audiences and messaging they plan to test.
• The Deliverables: What exactly are they going to do? Campaign setup, ad creation, weekly reporting, monthly strategy calls? It should be crystal clear.
• The KPIs: How will success be measured? This should go beyond traffic and include metrics like Cost Per Trial, Trial-to-Paid Conversion Rate, and a target ROAS or LTV:CAC.
• The Pricing: The fee structure should be transparent. Is it a percentage of ad spend, a flat retainer, or performance-based? There should be no hidden costs. If you're unsure what's fair, our guide to UK agency pricing breaks down the common models.
• The Timeline: What to expect in the first 30, 60, and 90 days. A good agency will set expectations that the first month is about testing and data gathering, with performance ramping up from there.

Now for the red flags. If you see any of these in a proposal, think very carefully before signing:

Red Flag #1: Long-Term Contracts. Any agency that tries to lock you into a 12-month contract from day one is showing a massive lack of confidence. A standard and fair approach is a 90-day initial term, which is long enough to get campaigns optimised and show results. After that, it should move to a 30-day rolling notice period. If they're good, you'll want to stay anyway.

Red Flag #2: Vague Promises & Jargon. If the proposal is full of phrases like "synergistic marketing," "brand amplification," or "growth hacking" without specific, measurable actions, run away. It's a sign they don't have a real plan.

Red Flag #3: One-Size-Fits-All Packages. If they offer "Gold, Silver, Bronze" packages without tailoring the proposal to your specific needs, they're a factory, not a strategic partner. Your business is unique and the strategy should reflect that.

Red Flag #4: No Direct Access. The proposal should clarify your points of contact. If you're going to be funnelled through a junior account manager who acts as a go-between, it's inefficient and things will get lost in translation. You should have a direct line to the person actually managing the campaigns.

Choosing an ad agency is a massive decision for any UK SaaS founder. It's not just about hiring a supplier; it's about finding a partner who is as invested in your growth as you are. Don't be swayed by a slick sales pitch or a low price tag. Do your homework, interrogate their expertise, understand your own numbers, and trust your gut. The right partner won't just run your ads; they'll provide strategic input, challenge your assumptions, and become an extension of your growth team.

Trying to do it all yourself or hiring the wrong agency is almost always more expensive in the long run due to wasted ad spend and, more importantly, lost time. If you'd like an expert, second opinion on your current advertising efforts or want to discuss how a specialist SaaS agency could help you scale, we offer a completely free, no-obligation strategy session. We'll take a look at your account and give you some actionable advice you can use, whether you decide to work with us or not.