As much as it annoys you when you get scammed it's all part of games. If everyone traded fairly and got along well what's the point? You have to make a few enemies or it just becomes dull.
Ata can always limit the about of money you can transfer within period of time. 1B ever 24 hours lol or something
I like the trading idea but not for money. I don't believe items you're getting for free should be sold. Even though yes I have in the past bought items.