Chiang Mai has quite a number of shops selling second-hand or used books. Several are in a small street branching off Tha Pae road, just east of the moat. You will find a wide collection of books at a reasonable price. It’s a great place to fill your library with all the classic “must reads” or to find something you may want to read while waiting for your plane or bus. Most of these shops will also buy back the books you have already read.
The used books shops in Chiang Mai are well stocked with a large collection of books; old and new. Just walk in and browse the shelves.