Lucky indeed. No lucky rabbits feet for the Fey today.
It's interesting to note how they look during the hunt. I'd take it that the Fey like to go big on the intimidation factor here.
Hmmmmmm...I'm still wandering about that deal they made with hell though. Things from hell and the Fey world are well noted for their trickery in deals, but why would either side make a deal with the other, what would they really be dealing over and what kind of power could either side have over the other to keep the other to the deal made?
Is it even a factor? I'd guess I'd be surprised by how much the stories got wrong as much as the stories got right.
I'd guess that the dealer from Hell and the dealer from the Fey both knew more about the other side than we know about either. Which suggests that they might know something about what to swear on, and how likely they are to keep said bargain...
... and, I should point out, the Fey are known in general to be very tricky, but to keep their word. Even if they bend the spirit of the agreement into pretzels. It's entirely your fault that you didn't know that the words they used had more than one meaning.
Hell, on the other hand, usually is shown as having little regard for agreements, unless they really really want whatever you're bargaining with, or they're being observed by higher powers.
So, in summary - it depends on which story you follow, but the preponderance of options suggests "it depends", even so. :-/