M.F.
First mistake was taking payments. When selling on Craigslist cash only, first come, no holds. I would either contact the buyer and ask if he would like his money back(full amount) and try to sell to someone else. Or try to work out a deadline of when it would be payed. I can see how this would be annoying but I would still give the full amount back and consider this a lesson learned. It's still cold so he could still sell it.