If you are intent on following through and selling, you should come up with a sliding scale. Maybe 1-2% for the minimum of what you'd sell it for, and a bigger

If you are intent on following through and selling, you should come up with a sliding scale. Maybe 1-2% for the minimum of what you'd sell it for, and a bigger percentage (10%) of the difference if he sells it for more. I don't know if that is standard practice, but it seems reasonable to me.