Here are the legitimate questions to ask:
1) Have you ever worked on this area? (Not are you "willing to do it," ACTUALLY done it.)
2) How many have you done? (A real number here ... not just, "Oh, I do that all the time!"
3) How long did the procedure take (averages)? (Not just, "Oh it takes about a year." You want a real number IN HOURS. You are paying for treatment hours. A reasonable average would be 4 - 10 hours, depending on the size of the area, i.e., if you are doing contiguous areas.)
4) Would you be willing to have one of your former clients talk to me about their experience?
These are reasonable questions. I answer these questions all the time. I encourage clients to ask such questions. And, yes, most clients will talk about their experiences to prospective clients. Get to the heart of the matter and avoid the "fluff talk!"