I really like this post-a-day from @raccoonmask and think it would be right at home at a Tribunal Fair. I won’t replicate the whole post, but Akakios offers the unusual bargains you’d expect from a faerie — trading your destiny for a stone of luck, or your fears for a gauntlet of might; with mechanics to match.
I think some of the bargains might have house rules, but nevertheless it’s good food for thought.