Good luck with the sale. Unless the prospective purchaser could demonstrate an acceptable number of hours and proficiency on type, or similar, then no, I would not let them test fly.
There are also specific insurance considerations to be checked out, prior to anyone flying your aircraft.
My experience has been that if the potential purchaser does not have enough experience, then he organises a suitably qualified pilot/instructor to come along, and if necessary for a purchase, fly the aeroplane. If they buy, then the purchaser can get whatever training he/she needs to after he owns the plane.
Also, there are occasions, similar to selling anything, where nosey pokes pitch up, just to get a flight, but I am sure you can weed those out on first contact..
