I always thought that Amazon is very strict with paying for reviews etc and I always thought I can comfortably buy something which had 4+ star reviews.
Recently I've been extremely disappointed, not only Amazon lets it, they do it on products which they sell on their own.
The way I spot it is very simple on every review you can see the reviewers profile with his recent reviews, almost each and every reviewer of these kind of products reviews 50 other items every single day!!! It seems like Amazon has a full operation of people who they send tons of stuff every day in exchange for 5 star reviews.
Amazon doesn't do it, it's the 3p sellers.
Why aren't they caught yet? I don't know, but that's how Amazon rolls.
I saw a new product from a Chinese seller gather 3200 unverified reviews within a few weeks.
Amazon deleted all the reviews, but the product and seller were unaffected. Now the seller is back up to 350 unverified reviews a few days later.
Chinese sellers seem to get away with the stuff way too often.