What are som possible curses or drawbacks a hag would put on a pc?

My players met a Green hag earlier and wanted to do something to increase their con. I gave them +2 con in return of disadvantage on all death saves and checks to stabilise regardless of other effects.

Now some sessions later my players tells me they want to visit the hag again, i dont know what they will ask for, but what are some possible drawbacks the hags will want in return?

Also, for every deal they make with the hag, i want the hags to also send them to a dungeon and retrieve something the hags cant themselves.