This reminds me of the hateful comments that plague YouTube. Most of them come from accounts that only ever post hate comments. Would it be so fucking hard to write a heuristic that tags users constantly getting their comments downvoted so that someone can review them? Then, if they fail the review, you mute them for 6 months, delete all their comments, but let them think their comments are still visible. Maybe let all the haters see each other's comments and reply to one another so they can live in their own parallel universe of hate. These problems are not hard to solve. There is a lack of will to solve them.
Vendors typically will pay above the cost of their product for a single good review.
Sorry, but that's not going to help at all. After Amazon banned incentivized reviews, pretty much all the sellers contacted the reviewers to buy products and then get reimbursed by PayPal. Sure, it's against the rules, but it's not being enforced.
They're not even hard to spot. I stopped doing incentivized reviews after the rule change, but I can see that a lot of the other reviewers are still reviewing a lot of stuff as verified purchasers. I know they're not real because I turned down offers from sellers to review the same products after the rule-change.
The worst part is that these reviews are even less honest than when incentivized reviews were allowed. Not all incentivized reviewers were shills (I tried hard to review stuff honestly - I would guess maybe a third of incentivized reviewers did as well). In the post-incentivized-review world, however, everyone who is participating an a verified purchase sham is giving 5 star reviews.
Source for that: https://www.washingtonpost.com/business/economy/how-merchant...
If you have a Facebook account, you can find those groups easily. Though you may have to search for obfuscations like "AZON".
Most if not all of the top-ranked incentivized reviewers already had longstanding communications with sellers via email.