I have said and done: I will pay you rather than the dentist if no cavities. 
This has worked with son but not rally with difficult child who has zero impulsive control.
I try to have things be HER choices.
difficult child, however, really does not connect consequences and actions like most people do. It is part of her illness.
I set boundaries on how much I can/will do without resentment. Like right now, she is very bored, I will buy her a movie pass vs. handing her the money.
I choose my battles majorally and try to keep the focus on my own self/reactions as much as possible.
Compassion
