Half Price Books is way over rated. (1) Has a lot of old, mangled paperbacks, mostly romance, (2) Current and best sellers are meager, probably picked over by the staff, (3) Bring in a current or best seller to sell and if you get a penny on the dollar, you're lucky. You would be better served to donate your books to Good Will and taking the tax deduction.
I used to go to this store a lot, but when they opened their Camelback location, it sure seems the way they financed it was to rip you off on the amount offered to buy your books and the quality of books in-store went way down hill.
My father-in-law had run in to the same problems, he being also a prolific reader, and he has quit going to Half Price Books.