Just to add to that I have know owners of 'unusual or rare' aircraft who are far more experienced than any instructor who may be asked to do a check ride. I mean who would be more qualified to give somone a check ride in a two seat Spitfire, an Instructor with 5, 000 hours on Warriors or the aircraft owner who has probaly 100s of hours on type.
I can remember being asked as a young inexperienced instructor to check a guy out in a Cessna 182 which I had never flown. When I said I have never flown a Cessna 182 the CFI said, " well you are an instructor arnt you?"