Steeldrifter,
I also do trading on eBay.
When someone sends me a check, I hold the items for up to 2 weeks for it to clear. I've been very lucky so far and have not had a check go bouncy bounce, but if it does happen, I'm going to change my policy.
I would email him and tell him that the check is unacceptable and ask him to send an MO instead. I would then return his check with the item when I received and cashed his MO.