Working in a bookstore, I sell books, ideally that's what I am there to do, but sometimes I also return books. With most publishers you cannot return a book until you've had it three months and then you cannot return it after a year. That's a nine month window of opportunity. You don't return books at Christmas, because things will sell then that never sell at any other time, but come January you have to assess. Am I going to return this, or am I going to keep hoping? The most important factor, of course, is sales. If no one wants a book there is no reason to keep it on the shelf.
I know some booksellers who look at every return (a returned book is simply called a 'return') as a failure. They shouldn't have ordered it, or as many copies of it, as they did. I am not one of those people. Returns is just a part of the job. But it isn't. Often when I return a book, I'll think to myself 'And I meant to read that one!' So I have a choice: let it go, or buy it. I seldom go through returns without buying something and when I oversaw returns for the entire store there were a few times when that meant hundreds of dollars out of my pocket. I'm a lot better now, but its just after Christmas and I am trying to economize. My shelves are full of books I still intend to read, and I might actually read, someday. But today I was looking at the books I was pulling and thinking, 'Hmmm, and I meant to read that one!' Its a trial.