Just whatever they can. (Score 1)

I usually just ask them for whatever they want to pay. I sometimes get $20 or I have gotten upwards of $200. I rarely have them call me again considering that I explain everything before I do anything. And ALWAYS explain that you are doing this for enjoyment and that you are not doing this as a business. That usually eliminates any view of doing something wrong on your part. It seems to be working pretty well. It might not be for everyone though.