In theory, that's what the eBay returns policy is for - you can state whether or not you will accept returns on items which you sell. For example, if I sell any used clothes or bikes/parts, I always state that returns will not be accepted unless the item is significantly not as described, and I make sure that the item description is 100% accurate.
This is true, but there seems to be a few folk who buy stuff, then decide after it's arrived that they don't want it, and so come up with some excuse and try to get a refund, like "I normally take shoe size x, but thought that these in x-1 might fit" Errr well they didn't did they, and that's not really my fault now, is it? (this is real and we've had others of a similar nature).
All of that said, I have bought hundreds of items of all sorts from ebay, and the only two real problems I can remember (other than my only dealings with China!) have been with cranks; one pair described as Middleburn RS8 that turned out to be RS4, where the guy did offer a full refund, and then the plonker the other night who did / didn't sell me some SRAM cranks.