Maybe not.  

A new study from Harvard finds that Amazon reviews (when you mash them all up) are as reliable as those from paid critics.  Via Gizmodo:

The study, carried out at Harvard Business School, analyzed the top 100 non-fiction reviews from 40 media outlets, including the New York Times, the Guardian and the Washington Post, between 2004 and 2007. The researchers then compared data from review aggregator metacritic.com to that from Amazon.

On the whole, there was broad agreement—when reviews were taken in aggregate— between critics and Amazon reviewers.

The study also found that Amazon critics were more likely to favor new writers, while critics were more likely to thumbs-up books from prize-winning authors.