I occasionally buy children's books on ebay; dh sells books on Amazon. I'm happy to chat to you about both tomorrow if you want.
Amazon take a fairly hefty cut, but you don't pay to list, and can leave items on there for long periods (6 months I think) and then immediately re-list if you want. There's not much market for cheap books, or very popular books, as Amazon charge the buyer quite a hefty postage fee. But dh sells obscure/hard to find/often out-of-print theological stuff, and sells quite a lot of books and sends them all over the world. He usually has about 100 books listed, and generally sells between 2 and 5 every week.
i ve had experiences of both and have found ebay the better of the two. imn my case i sell alot of childrens and chick lit. i ve found you sell items quicker and usually for higher prices on ebay. items on amazon seem to stay on there longer and just dont seem to shift unless they are of a really low price- no matter what the quality.. hope this helps