I've never (to my knowledge) had a review on Amazon rejected, and I've left very some negative reviews, including when I received counterfeit items.

I always thought the review scams on Amazon were more driven by the third-party sellers doing stuff like listing takeover, astroturfing reviews, bribing customers for good reviews, etc., but maybe I'm wrong. I have personally received multiple offers from third-party sellers of incentives to leave good reviews.