Not directly related to fake reviews, but about 2 years ago I got banned from leaving reviews. I had been an Amazon customer for 18 years at the time and always left honest reviews (good and bad). I had something like 700 reviews, some that were quite extensive. For some reason the Amazon bot decided I had done something wrong. The problem is Amazon will refuse to tell you what you may have done and no amount of e-mailing or calls will change their mind. Just Google "Amazon banned me for no reason" and see how often this happens.
The only thing I can think of is that I had bought an item (a drone battery) and some of the reviews had said that they received a fake knockoff. I know that sometimes the seller for the same item changes. So when I got mine and I verified it was genuine, I posted that the battery I got from XYZ vendor was the real deal. The next day I was banned.
Worse part is once you are banned from leaving reviews, you can not ask questions about an item either. Sure, you can create another account, but it just cheeses me off that all sorts of other fake review stuff happens, but they will ban a legitimate reviewer (who has been a customer for many years) just because some bot thinks you violated some rule, and then refuse to tell you why.
