I used to do it for My fathers lot and for dealerships. Doing it for my father was cake walk and I made a lot of money at it. Working for a dealership however for some can be very stressful. Your manager is always going to be on your ass, you will always have a quota to meet, and you have to have the gift of gab. If you dont have the gift of gab you can forget making money in the field. You need to be able to make sure you are the alpha male in every situation and can take control every conversation that pops up, make sh1t up on the spot, and make it sound as though you know what your talking about when you have no clue.
If you can do that you will make a great car sales person, I can do that, I was able to work the car lots against them. I would tell my customers of the car lots scam and what I was supposed to do to them, gain their trust, I would then have their trust find out what they wanted to pay and work my sales manager. I would come back and tell my customer I want you to point, shake your head, stand up as though your going to leave but sit back down. We would play the sales and finance team like this for about 30 minutes making them think they wont budge till I got them the numbers they came in looking for or damn close and made a sale. NONE of the dealerships I worked for caught on I was doing this to them, I made quite a bit of money at times. But it is also luck of who shows up on the lots as well. But after a few years of it you will get burnt up doing it. I found I liked working the service end and went into management in that field.
Again, you need to be able to sell a ice cube to a Eskimo, and spit on the customers and make them believe it is raining on them even though they can see your spitting if your going into the car sales field.
As for making money there are several way. Most of the time used is where most of it is at, but if your lot has tons of new cars that have been on the lot too long (few months) they will do spiffs and spins (fancy way of saying bonus). Can be as mush as $100-$2000 and those are the cars you try to push on a customer first when they are looking for new. A dealership will get punished from the manufacture for having too many new cars on the lot, and too many new cars sitting too long. Used cars your money is made based on how much they got the trade for, minus any work done to it, prep work, shop fees, and whats left you will get 19-29% of the profit. If they have a lot wrapped up in the trade, and it needed work you may not make noting but the bonus attached to it which could be $50.
But dont take me wrong it can be fun if you like being yelled at all the time, fast pace atmosphere, cold calling ups, and trying to shaft your customers. My suggestion to you is do what I did if your given the chance with your own office where the big bosses cant hear what your saying. Worked wonders for me.