Too many variables.....how many cars does the lot turn per month?? Is he a selling sales manger, or does he make a nut off of the other salespeople??? Seems to me if he diversified and grew HIS ( key word ) transport business, he would make much more than a sales manager at any lot.
A friend of mine has 15 or so car haulers, and he makes well over 250k a year, plus he is no longer on the road. Instead he runs the whole show from his office, and spends 2 days a week selling his services. If your friend thinks he would be a good sales manager, then he should be able to grow his own business via sales. Nothing worse than giving up the freedom that is your own business to go to work for someone else and help them realize THEIR dreams.