the 10 year rule, how common is it and how is it enforced

I have been asked how old my rig is over the phone and I just hang up. Its not my kind of place, and I would feel uncomfortable parking there. Our Class C looks like every other Class C of every year and unless they check out the door panel, I don't think they could tell the difference. I could tell them its 15 years old or 3 year and no one would be the wiser. I'm glad they ask, so I can chose not to go there.