In looking at some items on Amazon the other day, I noticed the button on Verified Purchaser Review and I fell in love with it immediately. The biggest complainant/question that most people have with Amazon reviews (in fact all Review Websites) is that most people who review a book are plugs, they have not purchases the book and our nothing more than a friend of the author or have an axe to grind with the book or product.
However this is now all gone away. Well done Amazon, Yelp maybe you can learn a thing or two from just. Just a thought.