I thought there was just a thread about this but I'm not finding it. Since the seller hasn't responded there wasn't a deal, so no welch. What I would do is send and save a message stating that you are withdrawing the "I'll take it" or offer. Does two things. First, if it was a comms issue, maybe the transaction can be completed. Second, if he comes back and says you welched, you have shown where you sent a withdraw statement.