We were given a collection of old books awhile back by a friend who had inherited them from another friend. He didn't read, but knew they were valuable, and knew we enjoyed books. He dumped the whole lot here, and we sifted through what we wanted, what we didn't want, and what we thought might be valuable and wouldn't want to put in a 'take a book, leave a book' box.
We finally got around to investigating(a couple years later), and some of these books fetch prices from several hundred to several thousand dollars online. Being as these are books we'd probably never read ourselves and could use the cash, we'd like to sell them. Question is, how does one go about doing this? Half Price Books doesn't give you beans, and I don't really know what the best way to do this is.