Pigcat, I wouldn't worry too much; I would buy them for him if he wants, but as long as he is clear that if there's a problem, it's not down to you. The main thing I do on Ebay is check feedback, and particularly negs. You can find people with a few negs, but can see sometimes that the negs may not be warranted, or can tell from the seller's follow up that they would have remedied the problem given a chance.
Anyway, Ebay is so slanted in the Buyer's favour these days that I think it's fairly easy to get your money back if you go through their complaints procedure.....if you're willing to spend that time on your friend's behalf.
And of course, check that any DVDs are for the right region.