Tea or Coffee?
I don't have the rules in front of me, but with well over 20 plays of Castle Panic, we play it as only one trade with only one player.
The expansion takes it to whole new level of pain. Good fun though!
Edit: And now from the rules, page 3, section 3, 'Trade Cards'.
Each player may make only one trade on his or her turn.
This is for the 2-5 player game. A 6-player game does allow two trades.