Things come up. Even in my case, there have been small emergencies that arise while I'm in the process of completing a transaction with someone.
For what you are suggesting: PbN has zero control of what other people do, so there is no way to regulate this "proposal". You, as a seller or trader, need to use your best judgement before starting the communication process between a possibly interested buyer. By looking at the user's feedback and their post history, you can usually get an idea of what their habits are.
SAMBROWN: He's a baller, a ladies man and most of all a stand up guy. I'd let him date my sister if I had one. So I guess my mother will do.
Auctionjunkie! : While most people consider ST to stand for Small Talk I feel it's more Septic Tank than anything else. It's where all the waste and refuge goes.