Even when Amazon reviews are legitimate, keep in mind that the reviewer may have been looking for something different than you are. Plenty of times I've bought stuff expecting one level of quality based on review scores, but got something less--all because I had a higher standard of what should be a 5 than most of the people who bought that.
one of the reasons why reading negative reviews is often helpful: there you often can figure out if the complaints about quality are from people with your standards or from people with higher ones. (after you filter out all the people who don't understand the difference between a product review and a review of their local postal service of course...)
The negative reviews far more often will tell me where the weaknesses and problems are so I can determine if they are things that matter to me.