I read about this via Dear Author initially, so credit to them for the story.
The basic gist is that there was an article in Paste Magazine about people returning e-books on Amazon, who has a 7 day return policy. Some authors only have a few returns while others have quite a bit- 10% of their sales. The article lists a bunch of people who believe that many of these returners are reading the book and then asking for their money back.
DA brought up a good point: many people aren't able to immediately read the books for whatever reason, so a return could happen days after the initial purchase. I have to add this tidbit: some people return e-books because the title was so awful that they didn't want to finish it or keep it on their reader. Sometimes people do it because a book is filled with so many visible errors that they can't bring themselves to read it and return it more to prove a point that someone shouldn't have to pay for a book where the author couldn't or wouldn't edit out the grammatical and spelling errors.
I have to admit that I'm not a fan of returning books (print or e-book) if you've read them. I don't think I've returned a book for any reason other than already owning it or getting the wrong one as a gift. I do think that there's a bit of an issue with the idea of getting a book and returning it later just so you could purchase another book down the road. Reducing or eliminating the amount of time one can get a refund would help, but I think that many authors would see reduced sales in general. Many of the people who do this purely as a way to get "freebies" aren't usually the type that want to spend money in general.