The incentive structure can get seriously misaligned if you receive the product for free. You want to keep getting free products, which means that you want to make the person giving you the products happy. Amazon is giving you the products. Amazon is happy, or at least there is a common perception to that effect, if you rate things highly because then more people buy things from them. So you rate more highly so that you can keep receiving free products.
Not only that but, IMO, you can't really objectively review a product you didn't pay for and buy out of your own free will. "That's neat" for a product you got for free can easily be "waste of money" if you had to pay for it.
Most product reviews you see by bloggers and youtubers are seeded this way. Vendors understand that when people are curious about a product, they search for it and click on some reviews. It’s common practice to make sure that they have results by giving them to reviewers.
Reviewers generally fall into 3 categories.
The small time reviewers who are excited to get free stuff, and want more free stuff in the future. Aside from their delight of free product, which gives a major positive bias before they even unbox, there is also the fact that if they trash a product, nobody is sending them one again.
Then there is the professional reviewer. They monetize their website and youtube channel heavily, and they live or die by getting product to review. If they trash a product, they face a huge risk of not receiving anything from that vendor again.
The third is the fully independent outfit that has a revenue stream completely detached from the product, and often have to buy it on their own. This is very expensive, and not many consumers pay for reviews. Consumer Reports is an example.
As a result, almost any kind of review you find is likely worthless, and should be treated as a paid ad.