When something is being repeated over and over again, it must be true. Right..?
When you need to convince customers of something, repeating your point (possibly from different angles and different media) will help you make the customer believe it's true. What will be even more powerful is having multiple sources confirming or repeating you claims. Of course it also helps if the claims are... you know, actually true :).
Recently I've seen some (often absolute) statements going around, generally in the line of "open source commerce platforms are a terrible idea". Now of course different solutions always have different pros and cons.
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.