The first time I bought an e-book from B&N, I got confused about what I was doing and accidentally deleted it and downloaded it again, therefore accidentally buying it twice. I was charged twice, emailed them about my mistake and that the two copies were bought within a minute of each other so obviously it was a mistake, and they credited my account for the second book.
Then, a long time later, I wanted to re-read a part of the book. B&N had deleted my copy of the book, saying I got a refund, so I couldn't re-download it. I emailed them about it and it was resolved, but there is not way to know whether this will happen again, and whether every instance will be easily resolved.
I guess it made me skittish. I appreciate them solving the problem, but I'm concerned that it was solved in the first place, and they apparently went back through my books at some point and found the credit and deleted that book. Why did the re-examine my books? I am uncomfortable with that. I shouldn't have to repeatedly explain that I paid for the book and we resolved it.