It's not like a trading system is all that difficult anyways. I've done enough GS1 scripting and seen enough GS2 to know that this is more than possible with an NPC-Server. If you were trying to make this in GS1, then I'd understand the excuses...
Just have them choose items to trade and/or gralats. Display them on both screens so that the users can see what have been entered. Have an agree button to lock the trade for both of them. Accept. Boom! Item traded. Think about the scripting that would require. :o Only problem I can foresee is duping, but that's what testing is for.