There are 3 second hand bookstores that I know of @House of Prose I love the discounts they have on books and wide selection. Also
@BookWorld they have books from the ceiling to the floor, although the conditions of the books vary from new to held together ranging from Dh5 to Dh50, but you get half your money back on every returned Book N Bean (also there is wiggle room to bargain) Lastly there is @Book N Bean A non-enclosed alcove in a large hardware store is an odd location for a book store, but the set-up at Book 'N' Bean is surprisingly nice even though it is inside ace hardware. The books are in excellent condition and easy to locate what book you want. Wifi is amazing and if you get there loyalty card after 9 book or coffee purchases your book is free!