“The going rate for having an Amazon employee delete negative reviews is about $300 per review, according to people familiar with the practice. Brokers usually demand a five-review minimum, meaning that sellers typically must pay at least $1,500 for the service, the people said […].
One Chinese Amazon seller said competition on the website had become so heated that he is tempted to use illicit tactics to gain an edge. “If I don’t do bad things, I will die,” he said of his business”.

Source : Amazon Investigates Employees Leaking Data for Bribes – WSJ