Amazon says it has systems that aim to prevent this manipulation. We're not suggesting that Amazon is at fault here and we should point out that the world's largest E-tailer is going to attract the most fraud attempts. That said, there are ways that Amazon could make it more difficult to game their system, at the cost of making honest comments taking more time to post. There's also the labor cost of verifying that the posts are legitimate.
Demonstrating again the downside of consumer product reviews on E-commerce sites, it was reported by The New York Times that some flowery comments on Amazon.com about the Carbonite online backup service were penned not by a happy customer but by an ethically-challenged Carbonite marketing guy. The revelation came shortly after news that a bold Belkin employee was actually paying people to write phony positive Amazon.com reviews about Belkin networking equipment.