You think someone who could manage to do that would waste there time hacking graal when theres other games that you can hack and make a real money profit out of it.

As for the trading system... one thing will just lead to the next:
staff:ok, we added a new trading system, enjoy!
public:it's too limited! you should add item hire!
staff:Ok, we added a loaning system, have fun

And so the cycle continues. If people really want to trade just do it with those you know and trust. Simple