When I'm producing a very low budget project, I ask crew members to think about the job offer and let me know their decision in the morning. That way, they can consciously decide to be all in or not in at all. Not every producer offers that, so, when I'm asked to work below my rate, I let the person offering know that I will meditate on the offer and get back to them in the morning with my answer.
It's just awful when you are told someone will do the job and then they don't because of resentment. You could have found someone else to do it with joy, but, the resentful person basically has your project held hostage. It's passive aggressive at it's worst. It's also awful to be on the hired end of that, resenting rather than enjoying your work. If you can't shake off that resentment, you've got to replace yourself.