First thing first....what was the name of the Buyer? Audiogon should be notified immediately so they can remove his Buyer status and hopefully, all future usernames coming from his email account. I know this easy to work around, but A'gon should still be notified. This is a long running scam. In a week, possible longer, the "check" will turn out to be fraudulent; the Buyer hoping you will cash him out before the ruse is discovered. Run, do not walk, to the nearest exit.
Jerry
Jerry