My sister just went through this last week. She made a king sized Trip Around the World with a wolf panel in the center. When someone saw it, they instantly wanted her to make them another. This thing took several months, as my sister works and does not have a whole lot of time. She quoted the person $1,000.00. That put an end to it.
As someone else said, once you have been able to say no, it gets easier to say it again.