To avoid being scammed, you just gotta be cautious. No trading while you're drunk, crying because your girl left you, and watching 90's sitcoms at 2a.m.
And don't trust people. When I first started with MMO's, I was just a wee lad with stars in my eyes. About 11 or so. I spent a lot of time saving cash monies in this one game, and then lent an expensive item to a guy who I had played with for quite a long time. A few months or so, which seems moderately long to me. He stole it right then and there, and I never saw the item again, and he never chatted me again. Just like that. My 11 year old soul was crushed, and I became a dark coal miner at heart. Gotta be cold if you want to avoid being scammed. Everyone is not your friend.