Yep -- I've gotten multiple postcards in the mail and/or product box after ordering something telling me I'd get ~$5-$10 if I left a 5 star review. They thoughtfully included exact screenshots of how to submit the review.
I also went looking for a way to report it. Eventually opened up a chat, didn't really get anywhere.
(I also didn't appreciate getting junk mail for ordering something).
you go to account -> customer support -> click the order -> chat... or fraud or somthing else