Do not buy or barter from fae. They are fickle and clever, and will trick you of your name or mind or heart. You may walk away not even knowing what you have lost. If a fae attempts to trade with you, thank them but walk away. Even if they offer you what you most need, be careful of even considering it, as all too soon the trade may be considered done, and something important will be lost.
Denying a trade may result in tears or a display of misery, but it is all games on the part of fae. Remain stony faced and carry on, and leave them to act out their part without an audience.