Some things lend themselves to sale on Amazon, others are better off with eBay. I sell most things on eBay, but for things like my old textbooks, I use Amazon. They take a much larger portion of the sale (15% + $0.99), but it's actually not that much higher than eBay once you combine the listing fee, the final value fee, and the Paypal fee (which, of course, goes to eBay). And of course, Amazon lets you list items for a full two months, eight times longer than eBay.
Anyway, I listed about 11 of my textbooks on Amazon. I have more, but I went through and some of them simply weren't selling for enough to be worth listing them. So I went through and listed each one for about a dollar less than the lowest-priced used one available. I sold three in less than a week! That's the best strategy, really... if you're not really greedy and just want to recoup a little money, Amazon is the way to go because you can undercut everyone else pretty easily.
Plus, eBay is now infested not only with scammers, but also people selling stuff for super low prices + ridiculous shipping charges. eBay doesn't collect their fees on shipping charges (other than Paypal of course), and they don't show up in the main auction listing. So in order to be competitive on eBay and get people to even notice your item, you have to either do the same thing as everyone else and sell it for a low price + insane shipping, or charge a much higher price and give free/reasonable shipping.