This means reading online feedback from other consumers is no longer a reliable way of checking the quality of goods and services.
Which? has received several reports from consumers who say they have been offered money by Amazon Marketplace sellers to remove negative feedback, according to the Telegraph.
Which? said the practice raises concerns that consumers are being misled about suppliers if previous customers are being paid to remove negative feedback.
The organisation has also received reports that some suppliers are refusing to resolve consumer complaints until the negative feedback is removed.
Amazon said reports of misuse of the feedback system are rare, but the practice will not be tolerated.