You are 100% oppening yourself up to abuse. Although, the idea is interesting and worth exploring you would need to make sure that your return policy was a bit heafty so as to make abusing the system a bit of work. Generaly people who want to abuse these kinds of things don't want to put any work into it and this would help to atleast syphon some of them out. You may also think about talking to the publishers and making people who wanted a return do a survey as to why they felt the book was bad and work out some sort of deal with the publishers to buy those surveys......just an idea
