AbeBooks - AbeBooks has millions of new & used books, rare books and out of print books.
eBay - Buy and sell electronics, cars, fashion apparel, collectibles, sporting goods, digital cameras, baby items, coupons, and everything else on eBay, the world's online marketplace
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Bibliotech - Bibliotech is the Spotify for textbooks.
Openbazaar - A free online marketplace to buy and sell goods / services using Bitcoin. OpenBazaar is a peer-to-peer ecommerce platform with no fees or restrictions.
BookLikes - BookLikes is a free blog platform for book lovers. 100% independent and free.