Make trades reversable for a short period of time
Much like the buy back feature. Trades using the trade window should be reversable. Here is how it would work:
1) You make a trade through the trade window
2) You have a screen where you can see your last trades. Lets say you only have 5 mins to reverse the trade. After this period the trades are final.
3) All items and gold are locked and can't be traded, sold or given away in those 5 mins.
So if you feel you have been scammed you have 5 mins to reverse the trade. And this should work even if the person changes their name or logs off. The only downside I see is that if the person has "buyers remorse" and not scammed they could reverse the trade. But ultimately, everyone gets their stuff back so no one should feel cheated.