Paid Reviews on Amazon?

All I know, is that a company named, Uteful that I purchased ink cartridges from on Amazon.com, sent me a letter promising me a $50 gift card if I would publish a 5-Star Review about their product. I decided to write a 2-Star review on Amazon because the company tried to bribe me. Well, I just got the email from Amazon denying to publish my review. Apparently, they are okay with this practice. So, don't trust Amazon reviews. They can be bought and sold.