I would give him 7 days, if there's no response sell to someone else.
I sometimes have this problem with repair jobs, someone will agree to send me a watch after exchanging a couple of PMs, I give out my address then I hear nothing and the watch doesn't arrive. Not quite the same but still annoying, if someone changes their mind about having a watch fixed or (in your case) buying the watch all it takes is an e-mail or PM to communicate, failing to do so is ill-mannered to say the least.