How to Choose the Right B2B Advertising Agency in London: A Vetting Guide

Finding the right B2B advertising agency in a place like London can feel like a proper mission. The market is saturated, and everyone claims to be the best. The truth is, it's not about finding the 'best' agency, it's about finding the *right* agency for your specific business, your customers, and your goals. A brilliant eCommerce agency might be completely lost with a complex B2B sales cycle. This guide will walk you through how I'd go about vetting an agency, based on my experience running campaigns for all sorts of B2B clients. It's about cutting through the noise and finding a partner that can actually deliver.

Where do I even start? It's a crowded market.

Honestly, the first place I'd look is their case studies. And I don't mean just glancing at the logos on their homepage. I mean really digging into them. Are they just showing off pretty ads with vanity metrics like '10 million views'? That's great for a luxury brand launch we did once, but it's probably not what you need for B2B lead generation. You need to see if they have real, tangible experience with businesses like yours. Are they working with other B2B companies, ideally in your niche or a similar one? If you're a SaaS company, do they have SaaS case studies? If you sell high-ticket industrial products, have they ever done that before?

Look for specifics. Look for results that matter to a business. I'm talking about leads, cost per lead (CPL), signups, trials, and if they can track it, return on ad spend (ROAS). For example, we've worked with a few B2B software clients where the main goal was getting qualified leads without breaking the bank. For one, we managed to get their cost per lead for reaching senior decision-makers down to $22 on LinkedIn. For another, focused on environmental controls, we cut their CPL by 84% using a mix of LinkedIn and Meta ads. These are the kinds of numbers you should be looking for. It proves they understand the B2B landscape and know which levers to pull.

You also gotta be realistic. If an agency's case studies all look too good to be true, they probably are. Every campaign has challenges. A good agency should be able to talk about them. They should be honest about the fact that B2B is tough and it takes time. They shouldn't be promising you the world. Tbh, in paid advertising, you can't really promise anything. The market changes, platform algorithms change, and it's impossible to predict performance with 100% accuracy. So look for an agency that presents realistic, verifiable results and can talk intelligently about how they achieved them. If their case studies are vague or all focused on B2C clients, they're probably not the right fit for you, no matter how impressive their client list looks.

Beyond the glossy case studies, how do I know they're legit?

Okay, so you've found an agency with some promising B2B case studies. The next step is to get on a call with them. This is where you really find out if they know their stuff or if they're just good at marketing themselves. A good initial consultation is not a sales pitch. It should feel more like a free strategy session. They should be asking you more questions than you ask them, at least at first.

They should be trying to understand your business inside and out:

-> Who are your ideal customers? Not just the company size or industry, but the specific job titles of the decision-makers.
-> What's your sales cycle look like? Is it a few weeks or six months?
-> What's the lifetime value of a customer? This tells them how much you can afford to spend to acquire one.
-> What are you selling, and what makes it diffrent from the competition?
-> What have you tried before? What worked and what didn't?

If they just jump straight into a presentation about how great they are without understanding your context, that's a massive red flag. A true expert knows they can't reccomend a strategy without a diagnosis first. This is exactly what we do in our own free initial consultations; we spend most of the time reviewing their existing strategy and ad accounts to give them some actual, helpful advice. That's the sign of a partner, not a vendor.

Then, it's your turn to ask questions. And you should ask some tough ones. Don't ask "Can you get me results?". Ask "How would you approach getting us results?". Here's what you should be digging into:

Which ad platforms would you prioritise for us, and why?
Their answer here will tell you everything. For most B2B businesses, the conversation revolves around two main platforms: Google Search and LinkedIn. A good agency will be able to explain the pros and cons of each for your specific situation. Are your customers actively searching for a solution like yours right now? If so, they should be talking about Google Search ads, targeting keywords like "AI implementation service" or "accounting software for small businesses". This captures intent, which is incredibly powerful.

If your customers *aren't* actively searching, or you need to reach very specific people (e.g., "Head of IT at FTSE 250 companies in the financial sector"), then they should be talking about LinkedIn Ads. LinkedIn's targeting is second to none for B2B. You can layer job titles, seniority, company size, industry, and even target a specific list of companies you want to get in front of. We once ran a campaign for a B2B SaaS client and used Meta ads to get 4,622 registrations at just $2.38 each, which shows that social can work, but it depends heavily on whether you can reach your audience there. A good agency will have a clear rationale for their recommendation, not just a one-size-fits-all answer.

What kind of funnel would you suggest?
For B2B, especially with high-ticket services or complex software, a simple "click ad, buy now" funnel rarely works. The sales cycle is longer, and trust needs to be built. The agency should be talking about lead generation. This usually means driving traffic to a landing page with a compelling offer—a free demo, a free trial, a whitepaper, a webinar, or a consultation. They should understand that the goal of the ad is to start a conversation, not to close a deal on the first click. The objective is to get a qualified lead into your sales process. If they start talking about complex, automated funnels that look more suited to a B2C eCommerce brand, they might not grasp the nuances of B2B marketing.

What are the big red flags I should run away from?

It's just as important to know what to avoid as what to look for. Over the years, I've seen some common patterns with agencies that under-deliver. Here are the red flags that would make me walk away immediately.

Red Flag 1: The Guarantee
This is the biggest one. If any agency guarantees you a specific ROAS, a certain number of leads, or a #1 ranking on Google, run. Run fast. As I said before, paid advertising is an auction in a constantly changing environment. No one can predict the future. An experienced professional will talk about realistic targets, benchmarks based on similar clients, and a process for testing and optimising towards a goal. They'll never, ever guarantee it. A guarantee is a sales tactic used by people who are more interested in getting your signature on a contract than in getting you sustainable results.

Red Flag 2: The "Full-Service" Trap
Be wary of the agency that claims to be an expert in everything: SEO, social media management, email marketing, PR, web design, and paid ads. While some large agencies can pull this off, smaller ones often can't. Jack of all trades, master of none. B2B paid advertising is a specialism. It requires a deep understanding of platforms like LinkedIn, long sales cycles, and how to speak to a professional audience. You want a specialist who lives and breathes this stuff, not a generalist who runs B2B campaigns once in a blue moon. Their team should be built of paid ad experts, not account managers who dabble. I've seen accounts managed by people who don't understand the difference between a lead gen form and a conversion campaign, and the results are always a mess.

Red Flag 3: A Reluctance to Get Technical
During your call, if you ask about specifics and they get vague, that's a problem. Ask them *how* they'd structure a campaign on LinkedIn. A good answer would sound something like this: "Well, first we'd define your Ideal Customer Profile. Let's say you're targeting CMOs at software companies with 50-200 employees. We'd build a primary campaign targeting those specific job titles and industries. We'd likely test a few ad formats—maybe a single image ad driving to a landing page against a video ad with a native LinkedIn Lead Gen Form to see which produces not just the cheapest, but the most qualified leads. We'd also build a separate retargeting campaign for anyone who visits the website but doesn't convert, and we could even upload a list of your target accounts to ensure we're only showing ads to the exact companies you want to work with."

A bad answer is: "Oh, we use our proprietary targeting methods to reach the right people." If they can't or won't explain their methodology in a way you can understand, they either don't know it themselves or they're hiding the fact that their process is basic. You should feel like your learning something from them, not like their hiding some secret sauce.

Red Flag 4: The Reference Game
This might be a bit controversial, but it's an honest take from my side of the table. If an agency has provided you with detailed, relevant case studies and you've had a deep strategy call with them where they've demonstrated their expertise, asking to speak to one of their current clients can be a red flag for the agency. Tbh, for us, it signals a lack of trust right from the start. We've already shown you the proof and given you free advice. A good agency's time, and their clients' time, is valuable. They can't have every single prospect calling their clients. A better approach is to check their online reviews on platforms like Clutch or Google. That's public feedback from a wider range of clients, which often gives a more balanced view than a hand-picked reference.

Okay, I've found a decent agency. What happens now? And what should it cost?

Let's say you've done your due diligence and found an agency that ticks all the boxes. What should you expect in the first few months? And how do you know if you're paying a fair price?

First, a reality check on timing. B2B advertising is not a tap you turn on for instant leads. The first month is almost always about testing and data collection. The agency will be testing different audiences, ad creatives, and messaging to see what resonates. You might not see a positive ROI in the first 30-60 days, and that's normal. A good agency will be transparent about this. They should be communicating with you regularly, showing you what they're testing, what they're learning, and how they're iterating on the strategy. It's a partnership. They need your feedback on lead quality to help them optimise. If a lead comes through and they aren't a good fit, you need to tell the agency so they can adjust the targeting.

The success of the ads also heavily depends on things the agency can't control. Your website and your offer have to be solid. I've had to have some brutally honest conversations with potential clients before. I remember one B2B software company that came to us because their ads weren't working. I took one look at their site—they were selling a complex accounting system with no free trial. Their main competitor was offering a 3-month free trial. No amount of expert ad management can fix a broken offer. A good agency should be able to spot these issues and advise you on them, even if it's not what you want to hear. Your looking for a partner who will challenge you, not a 'yes-man'.

When it comes to costs, it's the classic "how long is a piece of string?" question. It depends on your industry's competitiveness, how specific your targeting is, and the platform you're using. LinkedIn is generally more expensive per click than Meta, but the leads are often higher quality. A B2B lead on LinkedIn might cost you anything from £20 to over £100, depending on the seniority of the person you're trying to reach. But that might be a price worth paying if a single customer is worth £10,000 to you. Some of our campaigns for B2B software have seen much lower costs—we once got trials down to $7 each on Meta by finding a pocket of the right audience there. The agency's fee will usually be a monthly retainer or a percentage of ad spend on top of what you pay the ad platforms. In London, for a capable specialist B2B agency, you should expect retainers to start in the low thousands per month (£2k-£5k) and go up from there based on complexity and ad spend.

Ultimately, it's not about finding the cheapest agency. It's about finding the one that provides the most value. An agency that costs £4,000 a month but generates £40,000 in new business is a much better investment than one that costs £1,500 a month and gets you nowhere.

I've detailed my main recommendations for you below:

It's a lot to take in, and getting this decision wrong can be a very expensive mistake, not just in agency fees but in wasted ad spend and missed opportunities. It's a complex process that requires a lot of vetting and a solid understanding of what good looks like. Sometimes, bringing in a specialist who has been through this process hundreds of times can be the difference between burning your budget and building a profitable lead generation engine that fuels your growth for years to come.

That's where professional help can make a huge difference. If you're looking for an agency and want a second opinion on your current strategy, we offer a free consultation to review your setup and give you some honest, actionable advice. It's a good way to see if we might be the right fit for you, with no obligation.

Hope that helps you on your search!