I've started people on Tigers (Sky, II, and 60's) Doghouse (modified to extreame), and even went so far as to letting someone who had never flown fly my Zen 50.
The key here is make the plane fly relativly slow, and keep the throws on low, even lower than the recomended lows for the snappy planes. If you don't have the time and patience to teach someone on a well built Tiger, then most likely you are not a good teacher. A Tige that is well built will fly easy enough to let a 5 year old take the controls ( I've seen it).
I understand the "know it all" attitude is very frustrating and I don't like dealing with it either. I usually don't, but wanting to learn with something other than those ugly trainers is not a "know it all" attitude. It's ambitous, and confident.
You can tell the first day out if they can handle it. If they can't let them know.
By all means lets not turn away someone just because they come out with a non-standard trainer.