I've never bought a car from a used car yard or new car dealership, so I can't talk from experience.
In Australia, residential real estate sales contract have a mandatory 28 day minimum cooling off period. I don't know anything about commercial real estate, so can't comment on that.
In a way it makes some sense that the other large purchase(s) in life should have a somewhat protracted sales experience. If you could walk in to a car sales yard and just buy a car chip and pin style, I suspect things could go downhill quite rapidly.
I haven't really thought this through very much, so I'm wide open to head different perspectives.