I worked as a car porter in highschool. (92-93ish?) One of the guys that I got to know pretty well and was a top seller there had an 85k year. it was big for him. Said he did 50-60k on average. This was selling new Toyotas. However, he put alot of time into goofing off, didn't take many walk ins unless it was a prettyish female... One thing he had going for him, was he did work. Outside of work. He grew up in a middle class community, and knew everyone. Overall was a pretty personal, guy. He spent time at the local sports bars, and ran a book on the side. ..... What he did was network. Alot. He also exuded trust and likeability.
Then there were the guys who I think worked their rears off. Lots of time on the floor. Every walk in. Re arranging the lot to kiss some owner butt, and doing all the side stuff that needed to get done. I don't think the bottom rung did 35k on a decent year.
There were some inbetween.
That was just one lot, one type of car, and 20 years ago. I don't think it would be something I'd like to do. Especially when some poor working slob with a wife and kids, making meh money, trying to afford a mortgage walks in, isn't too bright and your job is to screw him on the trade in, and screw him on the financing, pretty much screw him as hard as you can, to make that money. I don't think I could do it. (not all are I'm sure.)
In regards to the part time thing. I dont' think so, especially in this sort of economy where people are looking for jobs. You might get a gig as a trainee, but they are going to want more than 40 I'd guess. We had one guy who was in college and started as a porter before my time. He was on a light work schedual, and a good salesman. He also had a good relationship with the owner, since he was a porter. He was being groomed for more.