Deseret Book does not buy or sell used books. If you are looking for used, out of print, or rare LDS books, here are some suggestions of places you can try contacting*:
Weller Book Works
607 Trolley Square
Salt Lake City, UT 84102
Phone: (801) 359-0460
For additional retailers you can do an internet search using key words "LDS used books". You can also try 3rd party sellers such as Ebay.
*Deseret Book does not endorse nor specifically recommend a specific out of print retailer or service