I've been to Bookman's a fair amount, both selling and buying. On the selling side, sure I feel a little stiffed, I know that the books I sell to them are sold at twice the amount. However, those are books that I know I no longer want, and are simply taking up space on my bookshelves. Selling them to Bookman's gives me a chance to recoup some of the initial cost, and also gives me an excuse to browse around and acquire other books.
The only reason I'm not giving Bookmans a full 5 stars is because... well... I'm somewhat of a snob... and I wish I didn't feel such a compulsion to clean myself whenever I walk out of there.