Show them the victims. People have come before, and will continue to wander in hence. They're pets at best, the toys that they play with until they break, and even then. They can do good things to them, they can do bad, they can do all the above and more- just show that people who underestimate or get on the bad side of the fey don't end up well.The reciprocity idea is a nice one. I feel like the party will be quite wary of accepting gifts, especially food. Is there a good way to highlight what would have happened had they accepted, to make them feel more of a rush when they refuse gifts?