Thanks for all the replies, folks. My situation is similar to Chad's. I bought about 12 posters from him, and one tube came in, one tube did not. I'm up against the deadline to file a paypal claim, and when I did, he freaks out and figures that I should pay him and that it's my problem if the posters get delivered, because he did his part by putting them in the mail (the Royal Mail, no less, more notorious than the US post office at losing and destroying shit). I told him that when the posters get delivered, he gets paid and I release the paypal claim. Suffice to say, he was a dick about it.
It seems the consensus here is that he's ok if you get your posters, but if you don't get them, or if they are damaged, he's not sympathetic.
I won't deal with him again. He was that much of a dick.