Website conversion optimization services, judged on method

Agencies with a verified published price

How to shortlist a conversion optimization provider

1. Check whether you have enough traffic to test at all. Split testing needs enough conversions per variant to separate a real effect from noise, and many sites simply do not have them. Ask a candidate to estimate how long a test on your key page would need to run given your current numbers. A firm that answers honestly, including saying you are too small to test, is worth more than one that promises weekly winners.
2. Agree one primary metric before any research starts. Pick the single outcome that decides whether a change was good: qualified enquiries, completed checkouts, or revenue per visitor. Secondary metrics can be watched, but only one settles disputes. Programmes without this agreement drift into arguing about which number to report, which is how a testing budget quietly turns into a reporting budget.
3. Ask to see a losing test written up. Any real programme produces losers and flat results, often the majority of them. A firm that can only show winning case studies is either very lucky or curating heavily. Reading how they documented a loss tells you more about their method than any success story, because it shows whether they draw conclusions from evidence or from taste.
4. Separate the fixes from the experiments. Some problems do not need a test: a checkout that breaks on mobile, a form that rejects valid phone numbers, a page that takes eight seconds to render. Fix those immediately and test the genuinely debatable changes. A provider who insists on testing everything is spending your traffic on questions that already have answers.

What the service includes, and what it does not

A complete engagement usually contains analytics review, session and funnel analysis, some form of qualitative input such as user testing or on site surveys, a prioritised hypothesis backlog, test build and quality assurance, statistical analysis and implementation of winners. Firms differ most in who builds the tests. Where the agency writes the code, velocity is higher and your developers are spared. Where they hand specifications to your team, cost is lower and the queue is your problem.

What is rarely included, and should be asked about explicitly, is the work after the test: rolling a winner into the production codebase so it survives the next release. Winning variants that live only in the testing tool decay quietly, and a year later nobody can say which of them are still active.

When speed and stability are the whole opportunity

For a large share of sites the biggest available gain is not a headline change but the page rendering faster and behaving predictably. Google's Core Web Vitals guidance sets out the thresholds it considers good, including a Largest Contentful Paint of 2.5 seconds or less, and it evaluates a site at the 75th percentile of real user page loads rather than in a laboratory. That framing is useful for a buyer, because it means the experience of your slowest visitors, often those on mobile networks, counts against you.

If a candidate's research phase does not look at performance data at all, they are proposing to test copy on a page some visitors never see finish loading. Ask how they would treat a case where the fastest available improvement is engineering work rather than a variant.

How these engagements are priced

Three shapes are common: a fixed price audit with a prioritised backlog, a monthly retainer covering a set number of tests, and a hybrid where a research sprint precedes an ongoing programme. Retainers are usually quoted by test capacity per month, so read what counts as a test and whether build time is included. Performance based pricing exists but requires shared measurement both sides trust, which in practice means it suits ecommerce far more than lead generation.

Treat any published starting price as the floor for a single site, single template engagement. Multiple templates, multiple languages, or a stack where the testing tool cannot be installed cleanly all move the number up before any research has happened.

Questions people actually ask

How long should a test run?

Until it reaches the sample size agreed in advance and covers full business cycles, usually at least one or two complete weeks so that weekday and weekend behaviour are both represented. Stopping a test the moment it looks like a winner is the most common way programmes generate results that fail to replicate once the change ships.

What if my site has low traffic?

Then buy research rather than testing. User testing, session review, customer interviews and fixing outright defects all produce gains without needing statistical power. A good provider will tell you this and price accordingly. A weaker one will sell you a testing retainer that cannot conclude anything within the contract term.

Does conversion work hurt search performance?

It should not, provided variants are served to users the same way they are served to crawlers and the testing tool does not slow the page materially. Problems arise with client side tools that delay rendering or with tests that hide substantial content. Ask how the provider handles both, and insist that performance is monitored during a test rather than after it.

Who should own the testing tool subscription?

You should, in an account under your own business, with the agency granted access. The test history is a record of what your customers do and it is the most valuable asset the engagement produces. Losing it at the end of a contract means the next provider starts by asking the questions this one already answered.

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