CRO Agencies: What They Do and When You Need One

A CRO agency specialises in improving the percentage of your website visitors who take a desired action, whether that is making a purchase, submitting a form, or starting a trial. They combine qualitative research, quantitative analysis, and structured experimentation to find and fix the gaps between your traffic and your revenue.

Not every business needs one. But if you are running meaningful traffic volumes and your conversion rate is not moving, the problem is rarely what you think it is, and an outside perspective with the right methodology can be worth considerably more than another round of internal brainstorming.

What Does a CRO Agency Actually Do?

The honest answer is: it depends on the agency. The term “CRO agency” covers a wide range of operators, from boutique specialists running rigorous A/B testing programmes to generalist digital agencies who have added conversion optimisation to their service list because a client asked for it.

At the credible end of the market, a CRO agency will typically start with research before they touch anything. That means heatmaps, session recordings, user surveys, funnel analysis, and interviews with your actual customers. They are trying to understand why people are not converting, not just where they are dropping off. The where is visible in your analytics. The why almost never is.

From that research, they build a hypothesis backlog: a prioritised list of potential improvements ranked by expected impact, confidence, and ease of implementation. Those hypotheses become tests. Tests generate data. Data informs the next round of hypotheses. That cycle, done properly, compounds over time.

I have sat on both sides of this relationship. When I was running agencies, we had clients who wanted to skip the research phase entirely and go straight to testing because they had already decided what the problem was. That almost never worked. The clients who gave us the space to do the diagnostic work first were the ones who got the meaningful results. The ones who came in with the answer already written were paying us to validate a guess.

For a broader picture of how conversion optimisation fits into the performance marketing ecosystem, the CRO and Testing hub on The Marketing Juice covers the full landscape, from testing methodology to analytics frameworks.

When Does Hiring a CRO Agency Make Commercial Sense?

There is a traffic threshold below which CRO agencies cannot do their best work. A/B testing requires statistical significance, and statistical significance requires volume. If you are running a few thousand sessions a month, you will wait months for a test to reach a conclusion, and by then the market may have moved.

The general rule is that you need enough traffic to run tests that reach significance in a reasonable timeframe, typically two to four weeks. Below that threshold, you are better served by qualitative research and expert review than by a full testing programme. That is not a failure state. It just means a different type of engagement is more appropriate.

Beyond traffic volume, the other trigger is a gap between what your traffic should be doing and what it is doing. If your paid search campaigns are driving qualified visitors and your landing page conversion rate is well below what comparable businesses see in your category, that gap has a cost you can calculate. A CRO agency’s job is to close it. Unbounce has written clearly about the relationship between traffic quality and conversion performance, and it is worth reading before you assume your conversion problem is a page problem.

The third trigger is internal capacity. CRO done properly is time-intensive. It requires analytical rigour, research skills, copywriting, design, and development, often in the same week. Most marketing teams do not have all of those capabilities sitting idle. An agency brings the full stack without you having to hire it.

The Difference Between Good CRO Agencies and Expensive Ones

I judged the Effie Awards for several years. One thing that experience reinforced is how easy it is to confuse activity with effectiveness. The marketing industry is very good at producing impressive-looking work that does not move a business number. CRO agencies are not immune to this.

The expensive-but-not-good agencies tend to share a few characteristics. They lead with tools rather than thinking. They talk about their testing platform, their heatmap software, their proprietary dashboard, before they have asked you a single question about your customers. They present test results without explaining what they learned. They optimise for test volume rather than test quality. And they renew retainers by showing you a long list of tests run, rather than a clear line between their work and your revenue.

The good ones operate differently. They ask uncomfortable questions early. They push back on your assumptions about why your conversion rate is low. They are honest when a test is inconclusive. They build internal capability in your team rather than creating dependency. And they can show you, in plain numbers, what their work has been worth.

Moz’s CRO playbook is a useful reference point for what a structured approach to conversion optimisation actually looks like in practice, and it gives you a reasonable benchmark for what to expect from a credible agency engagement.

One question I always recommend asking in agency selection: “Show me a test that failed and what you did with that data.” A good agency has plenty of those stories and is comfortable telling them. An agency that only shows you wins either has not been doing this long enough or is curating the narrative.

How CRO Agencies Are Structured and Priced

Most CRO agencies operate on retainers, and the retainer structure tells you something important about their incentives. An agency paid on hours has an incentive to run more tests, write more reports, and hold more meetings. An agency paid on a fixed monthly fee has an incentive to be efficient. An agency paid on performance, typically a share of revenue uplift, has an incentive to focus on the highest-impact work first.

None of these models is inherently wrong. But you should understand which one you are signing up for and what behaviour it is likely to produce. I have managed agency relationships across all three models, and the performance model sounds attractive until you realise how much time gets spent arguing about attribution. Fixed retainers with clear deliverables and regular reviews tend to produce the most productive working relationships in practice.

On pricing, the range is wide. Smaller specialist agencies might work for £3,000 to £6,000 a month. Larger, more established operators with senior practitioners on your account will typically start at £8,000 to £15,000 a month and go up from there. Project-based engagements for audits or specific conversion sprints can run from £5,000 to £25,000 depending on scope.

The number that matters is not the monthly fee. It is the ratio between what you are paying and what the work is worth if it succeeds. If your average order value is £200 and your site converts at 1.5%, moving that to 2.5% on meaningful traffic volume is worth real money. Model it before you negotiate the retainer.

What CRO Agencies Cannot Fix

This is the part that does not get enough airtime in agency pitches. CRO has limits, and understanding them upfront saves everyone a frustrating engagement.

CRO cannot fix a product problem. If your product does not meet the needs of the people arriving at your site, no amount of page optimisation will compensate. You might lift conversion marginally by reducing friction, but you will not fix a fundamental mismatch between what you are selling and what your visitors want.

CRO cannot fix a traffic quality problem. If your paid campaigns are driving the wrong audience, or your SEO is pulling in visitors at the wrong stage of their decision process, your conversion rate will reflect that. Understanding where your traffic sits in the funnel is a prerequisite for understanding what you can reasonably expect it to do on your site.

CRO cannot fix a pricing problem. If your price is materially out of step with the market and your visitors know it, that is a commercial decision, not a UX problem. I have seen clients spend six months and significant budget testing landing page variants when the real issue was that their competitors were £30 cheaper for an equivalent product. The agency did good work. The business problem sat elsewhere.

And CRO cannot fix a trust problem quickly. If your brand has a reputation issue, or your site simply does not look credible to first-time visitors, testing will surface that insight but fixing it takes time and investment beyond the scope of a conversion programme. Hotjar’s ecommerce CRO resource covers how qualitative research can surface trust barriers that quantitative data alone tends to miss.

How to Evaluate a CRO Agency Before You Sign

The evaluation process for a CRO agency should be more rigorous than for most other marketing partners, because the work is inherently technical and the results take time to materialise. Here is what I would look at.

First, ask about their research methodology. How do they diagnose conversion problems before they start testing? If the answer is primarily quantitative, that is a gap. Good CRO requires understanding why people behave the way they do, and that requires qualitative methods: surveys, interviews, session recordings, and direct customer conversations. Unbounce’s compilation of how CRO experts would spend four hours optimising a site gives you a useful sense of how experienced practitioners think about prioritisation.

Second, ask about their testing velocity and what determines it. Some agencies run as many tests as possible. Others run fewer, higher-quality tests. Neither approach is universally right, but the agency should be able to explain their philosophy and why it fits your situation.

Third, ask about their relationship with your development team. CRO requires implementation, and if your developers are already stretched, a testing programme that creates a backlog of implementation work will stall. The best agencies have thought about this and have options for working around it.

Fourth, ask what success looks like at six months, twelve months, and twenty-four months. An agency that cannot answer this clearly has not thought hard enough about your business. An agency that answers with vanity metrics rather than revenue outcomes is telling you something important about their priorities.

Fifth, check their case studies carefully. Not for the headline numbers, but for the narrative. Do they explain the problem they were solving, the hypothesis they formed, the test they ran, and the learning they took from it? Or do they just show you a percentage uplift with no context? The former tells you how they think. The latter tells you how they sell.

Building Internal CRO Capability Alongside an Agency

One of the most commercially sensible things you can do when working with a CRO agency is use the engagement to build internal capability at the same time. This is not a threat to the agency relationship. It is a sign of a mature partnership.

When I was scaling an agency from 20 to just over 100 people, one of the things I noticed was that the client relationships that lasted longest were the ones where we were genuinely transferring knowledge, not just delivering outputs. Clients who understood what we were doing and why could have better conversations with us, challenge us more productively, and make faster decisions. The relationships that felt most like dependency, where the client had no idea what we were doing or why, tended to be the most fragile.

For CRO specifically, that means making sure someone on your team understands the testing methodology, can read the results independently, and is building the institutional knowledge of what has been tested and what was learned. That knowledge base is a commercial asset. If your agency relationship ends tomorrow, you want that asset to stay with your business.

Moz’s piece on turning traffic into revenue is worth sharing with your internal team as a foundation document. It gives a clear framework for thinking about the relationship between acquisition and conversion that tends to get siloed in most marketing departments.

If you want to go deeper on how testing, analytics, and conversion strategy connect across the funnel, the CRO and Testing section of The Marketing Juice covers the full range, from methodology fundamentals to how to structure a programme that actually compounds over time.

The Retainer Review: What to Measure at 90 Days

Most CRO retainers run for a minimum of six months, and that is reasonable. Conversion optimisation is not a quick fix. But 90 days is enough time to assess whether the engagement is on the right trajectory.

At 90 days, you should have a clear research phase completed. You should have a prioritised hypothesis backlog that reflects real insight into your customers and your funnel. You should have at least one or two tests either completed or in flight. And you should have a reporting cadence that gives you visibility into what is being tested, what the results are, and what the agency is learning.

If at 90 days you are still waiting for the research phase to conclude, or the hypothesis backlog is thin, or the reporting is opaque, those are signals worth taking seriously. Not necessarily signals to end the engagement, but signals to have a direct conversation about pace and process.

The metric that matters most at 90 days is not conversion rate. It is learning velocity. Are you understanding your customers better than you did three months ago? Are the hypotheses getting sharper? Is the agency demonstrating that they understand your business, not just your website? If the answer to those questions is yes, the conversion rate will follow. If the answer is no, that is the conversation to have before month four.

Hotjar’s Shopify CRO guide is a useful reference for ecommerce teams thinking about how to structure their measurement approach alongside a testing programme, particularly for teams where the analytics setup is still maturing.

About the Author

Keith Lacy is a marketing strategist and former agency CEO with 20+ years of experience across agency leadership, performance marketing, and commercial strategy. He writes The Marketing Juice to cut through the noise and share what works.

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