the most common way to scam people that i have seen is to post a ref and get someone to buy it, when tehy open trade the buyer pust in money and the scammer puts in a item that looks like whatever they are fake sellin, and hit accept very quickly, therefore the buyer cant shift-click on the item in trade,
i think it would be a good idea to make it possible to shift-click a item in trade even after somoen has hit accept.