I have bought a couple of books from Fictionwise and never encountered any problems. However, you should take a look at
this post from a guy who has been a Fictionwise club member for many years. His recently purchased e-book was virtually unreadable and the customer service from Fictionwise didn't handle this situation very well:
Here's part of Fictionwise's response to my request for a replacement: "I have confirmed the problem with this eBook. I have sent an urgent note to the supplier requesting that this be fixed. I will let you know when they respond." Can you imagine this response from any bookseller in the world? If the print was smeared or garbled on a paper edition, would the bookstore owner ask me to be patient while they sent the book back to the publisher and hoped that a new copy would arrive sometime soon? Wouldn't they just hand me a new copy and an apology?
Like I said Fictionwise was always OK for me, but this makes me reconsider where to buy e-books next.