OMG Iris, that is terrible!! I had a nervous moment when I was
transferring credits to a DISer because the amount was substantial.
I used a "secret word" that I made sure the other player knew in the
trade window as the task to "win" the quest, and I made sure it was
set on the non-timed setting, as well.
But when a friend came by when I didn't close off the entrance, I was
a little abrupt to tell them that they couldn't do my quest. The friend
left before I could explain I'm trading credits, but after I sent a PM, it
was all good.
I think that if you're doing this, I would suggest:
Don't open the quest machine until the other player who will 'win' is
in the room AND has the correct answer to the quest. After the
player is in the room, close off the quest area around you and the player.
THEN go and open the quest to the player. Even if you needed to repeat
the answer out loud (for whatever reason), if nobody else can get to the
quest machine, it won't make a difference.