I've never really had a "good" quality case come from the cheap options on eBay.
The thing I really don't care for on eBay is that it's not that easy to see reviews. At least on amazon, you can get a better idea of whether or not you are looking at a quality product. Not to mention that eBay's interface is preposterously old. I have very few things that I actually buy on ebay, almost completely because it's usability is a pain in the neck.
I would just stick to cases that are available on amazon. The amazon system puts the most frequently purchased/highest rated/best priced books on the top of the lists. eBay doesn't really do too much of that.