Ebay has twelve categories of book stores, so you can narrow your search to the type of books you are looking for. Some have only books while others carry other items as well.
There are so many book sellers on Ebay that it would be impossible to list them all. Here are a few that stand out in their respective categories. Once Upon a Time Books is a great place to shop for children's books with over 1,000 listings in that category. If you are looking for antique and collectible books, check out Princeton Antiques Bookshop. In addition to maintaining a large inventory, they are able to help you locate it out of print books. Ebay is also a great place to find textbooks. BuybackExpressSales is an example of a shop that both buys and sells textbooks.
Some book sellers on Ebay have a higher purpose in mind for their book shops. PhoenixFriends Store is operated by Friends of the Phoenix Public Library. 100% of the proceeds from sales in their Ebay store go to support literacy efforts in the Phoenix area. SeattleGoodWillBooks is a similar store that uses proceeds to provide job training and basic education programs in Seattle.