It could have been a sample that was provided and the prospect ordered. It could have been the testimony of another person as to what the product or service did for them. It could have been any number or combinations of things. But what it wasn't't was that the product sold on its own. The power of words in print are enormous.
People have a strong tendency to believe the written word.
If it's written and it appears to have some level of documented proof, people will more likely believe it. You've probably heard that a picture is worth a thousand words. But if you show a picture without explaining it, the interpretation of the picture will be left to chance. On the other hand, if words are printed on the page without a picture, and the words explains how the picture is suppose to look, then you can get a clearer and more graphic depiction of what the author is trying to say. With a thousand words you can describe a picture and what it is suppose to mean.