I saw a video where a guy did an incredibly thorough review of a product. Just a guy who bought something that didn't have a lot of reviews, so he threw together a video in his garage and backyard.

Eventually it got to the point where he had one of the top videos when you look up the product name on YT. A bit later the company sent him a bunch of their other products and he reviewed them. It's smart for the company to do that, but it makes the subsequent videos feel just a bit tainted.