Good question. I'm still waiting for the seller to contact me. Tough situation for him... I once made a similar mistake, but I caught the package at the post office before it went out.

In the past, when I have had a problem with a seller, eBay basically says "ship it back, we'll make you whole." But that requires that I again front the money to ship the package. Plus it effectively punishes me for the other guy's error.