Yeah you don't really need to worry so much about the manner car buyers are driving the car, because as you said, usually theres a salesman sitting next to you.
However if you think the car sits in the yard and is only driven on test drives, you are wrong. Salesmen use them as drive cars, to the shops, on errands, and to get to and from home, and I've seen them flogging them on a number of occasions.
Yes ok, the ones with very low km's, like under 100kms you are most likely pretty safe, just saying be cautious on your purchase, don't think, she'll be right mate, good as new, make sure it is so.
I guess I sound pretty pessimistic, I don't meen to be, just don't like it when people that don't know any better, get taken advantage of, myself included.