I Like The Idea of Amazon Verified Purchase in Reviews Section
If you browse amazon reviews chances are you already saw this Amazon Verified Purchase label. This is not a new feature, I think it's been there for a while but I just want to point that out.
It's easy to understand, it means the reviewer purchased that item at Amazon, could highly increase the credibility of the review.
I think it's easy to implement, the logic is simple but it's a good indicator for users to decide if they should follow or trust the review.
Also I tried it myself. When I click to write a review for the book I bought on Amazon, I get this option to choose if I'd like to label myself as purchased the item.