Used Books for Sale
Trading books websites:
1.http://www.titletrader.com/You have to TRADE the books so when you are finished with a book and want to get a new one, you can send out your book to someone who needs it and you get points to get a new book.
Used Book Buying:
1.Ebay! http://www.ebay.com/If buying a series I look for a lot with as many of the books in one auction. Less Shipping Costs. I save the search and if it is not a series I just have to have RIGHT now, I will watch for the best deal for me.
2.Amazon http://www.amazon.com/I found amazon for me to usually be cheaper than Barnes and Noble. Also they sometimes run a 4 for 3 special. you get 4 books for the price of 3. If you look at the book, under price some books say Special Offers Available. Click on that, and it will tell you this item is eligible for what promotion. I found that with the over $25 = free shipping and "no tax" it makes for some really good deals so that new comes cheaper than used!
4.http://www.abebooks.com/ I can sometimes find books autographed by the author on this site. But each book is listed seperately and you can pay shipping on each book, depends on the Sellers