I have sold on ebay for 5 plus years and have had only a few problems with bad checks. Usually, the bidder has made an honest mistake and they are willing to take care of it quickly, sometimes through paypal or even cash. I would wait out a response. Also check his feedback. If he has high feedback and good feedback, you know he is honest, something just went wrong with the bank. Keep emailing him though. It should work out most of the time.