Amazon Deletes Reviews That Mention Pay-For-Play Review Schemes

Interesting nuance (oldie but goodie): on the same Consumerist, Alex Chasick writes:

After buying an anti-snoring mouthpiece from a third-party seller on Amazon, reader Bob received an email from the company offering him a free mouthpiece in exchange for a five-star review. He noted this attempted bribe in his Amazon review, and Amazon deleted it. Twice. [...]

This is totally new to me. Check it out, quite curious.