We home stagers ALWAYS need hardcover books in some capacity for our projects. Most homes have built-ins or shelving units that need some adornment and books add a cozy warmth to a bedroom or office. Most of the time we need books to add a splash of color but not all books will work. Don't assume that potential buyers won't look at the hardcover's spine and see what kind of content you have on your shelves. Books on death, witchcraft, illness, medical disorders, criminal behavior, mental illness or even home staging might be a turn-off to buyers...you think?
Even book store sales can cost you a bundle if you need a LOT of books. I happened upon a nifty book sale the other day right in my neighborhood and I'll bet there will be one close to you too! Contact your local library to see if they are planning a sale anytime in the near future. My library in West Linn, OR lends and sells used books and I scored this collection below for $2.00 on the last day. I took all the covers off because if you look closely you'll see a biography on Steve Allen and a Weight Watchers Cookbook.
Good luck book-hunting!