There are review programs that act as a middleman between the buyers/reviewers and sellers that aggregate multiple items to review from many sellers. They could

There are review programs that act as a middleman between the buyers/reviewers and sellers that aggregate multiple items to review from many sellers. They could easily circumvent something like that (for example, if you want to participate, you get to buy 5 cheap shit items with a 90% discount from different sellers and have to leave 5-star reviews.) I think the first step would be not accepting reviews, or downranking them, similarly to unverified purchases, if the purchase was discounted with a promo code given by the seller.