Bad reviews are commonly deleted. The merchant can't do it themselves any more, but they get admin to do it all the time. As someone previously mentioned, the most common excuse is that the review mentions technical issues. You're supposed to get tech support from the merchant privately, not mention it in a review. (Never mind that the merchant may ignore you completely, refuse to fix their product, or simply not know how to fix it.)

For a few weeks after they changed the rules, reviews were truly honest. Then merchants found the loophole, and it was back to the same old B.S.