Amazon took another unconventional step when they started allowing third parties to sell the same items Amazon sells alongside the listings in their catalog. What other business has opened up their billing and inventory systems to anyone and everyone—including competitors? It may seem counter-intuitive, but Amazon is getting a small percentage of every sale. With thousands of transactions, that small percentage adds up quickly.
By using their site to connect both buyers and sellers, Amazon has enabled many entrepreneurs to sell through the Web without developing their own billing and marketing infrastructure. Other Amazon customers are also selling through their site. A box of books in the closet or a stack of CDs that no longer make it into rotation would otherwise continue to take up space. Instead, you can list them through Amazon, find people who are looking for exactly those items, and make some money.