Case studies belong in your decision, but they should not carry it alone. A case study is the company telling its own story about its own best work. That makes it useful evidence and unreliable proof at the same time. The right approach is to treat case studies as one input, read them critically, and weigh them against references, direct conversation, and the company’s proposed plan for your specific situation.
What a case study can and cannot prove
A good case study can show that a company has handled a problem similar to yours, has a process it can describe in concrete terms, and can connect its work to a measurable outcome. That is worth something. It tells you the company has done real work and can talk about it without vague language.
What a case study cannot prove is that the same result will repeat for you. The outcome in any SEO project depends on the starting site, the budget, the competition in that market, the timeline, and factors outside the company’s control, such as search engine changes. A case study rarely lists all of those conditions. So a strong result is a sign of capability, not a forecast of your result.
Read for relevance first
Before you are impressed by a number, ask whether the example resembles your situation. A company that grew traffic for a large national brand may have done excellent work, but that says little about how it would handle a small local business, or the reverse. Look at the industry, the company size, the type of website, and the competitiveness of the keywords. If none of the published examples look like you, that is a meaningful gap. Ask directly whether they have done work closer to your case, even if it is not published.
Watch for what is left out
Case studies are written to persuade, so notice the missing pieces. Common omissions include the budget, the full timeline, the starting point before the work began, and what else changed during the project, such as a new website or a separate ad campaign. A chart showing growth is not useful if you cannot see where the line started or how long the climb took. If a case study reports rankings or traffic but never connects them to leads, sales, or revenue, treat that as a limited result, since traffic alone does not pay for the service.
The survivorship bias problem
A company publishes its wins. It does not publish the projects that stalled, the clients that left, or the campaigns that never moved. So the case studies you see are the survivors, and they make success look more routine than it is. This does not mean the published work is fake. It means the sample is incomplete by design. To correct for it, ask the company about a project that did not go as planned and what they learned. A company that can answer honestly is showing you more than a polished chart can.
Use case studies to start questions, not end them
The most practical use of a case study is as a conversation starter. Pick one and ask the company to walk you through it: what the situation was, what they decided to do and why, what they would do differently now, and whether you can speak with that client as a reference. Their answers tell you how they think, which matters more than the headline figure. A company confident in its work will welcome these questions. Hesitation or vague replies are a signal in themselves.
A reasonable way to weigh them
Treat case studies as supporting evidence rather than the deciding factor. Let them confirm that a company is worth a deeper look, then base your final choice on relevance to your goals, the clarity of the proposed plan, reference conversations, transparent reporting, and how the company communicates with you. If two companies present similar case studies, the one that explains its reasoning and adapts its plan to your situation is the safer choice. Case studies show what a company has done. They do not, on their own, show what it will do for you.