The true problem is that users don't take the right precautions into preventing themselves into being scammed and I am not sure that there is a true way to really stop that. All these solutions will accomplish little to nothing. Contact information that a buyer/seller/trader needs to obtain is a lot more than email or aim address which is something that is stressed by PbNation.
Users need to take responsibility for themselves when dealing online. If all users followed the tips here http://www.pbnation.com/showthread.php?t=1620968
then almost all scams would be eliminated. PbNation has provided tips and the people need to take the responisbility to read them and that is where the true problem lies.