Mine did not accept payment for a rescheduled session due to double booking, which was the right thing to do, especially since I drive from another town and the whole thing took about 4 hours of my day, plus gas. I think there was one other time she offered to waive payment, but I can't remember why and I did not accept the offer and paid anyway.

Waiving payment doesn't make up for things that are not recoverable--like time (if there's rescheduling)--but it's a good thing to offer. It shows an effort to take or share responsibility.