I bought a $50 item and a couple of weeks later I received a letter in the mail offering me a $35 Amazon gift card if I leave a 5-star review with a video or picture attached. I'm surprised Amazon allows these kinds of bribes.
I reported one of these attempts to Amazon customer support once and the response I got back was basically "if we catch you accepting payment for positive reviews, we'll ban your account and you'll lose all of your digital purchases." No questions about the seller or the item, just a veiled threat.