I mentioned that I'd had to give a refund on a Mac Mini I sold on eBay that was returned to me with the Wifi defunct. Brian WINOLJ suggested I make a claim for compensation from Collect+, the courier company I used. It turned out that when I added everything up I was out £47.07; the original postage, a refund for postage I gave to the customer because it was DOA, and the money I lost by it selling for a much lower price when I relisted it. To be honest, I thought that I'd be lucky to get the cost of posting back because there was no obvious damage to the outside of the package, but following several emails and a letter (sent recorded delivery to make it clear I was serious) they're going to send me the full amount!
The moral, I think is that if you don't ask you don't get.