Sales is a tough gig to get into, especially when you first start off. Typically you make nothing to start, and have to build up clientele from there, aside from the occasionally drop of luck...which won't happen often since the people who have seniority over you are going to get treated better.
There's plenty of jobs out there where you can make a lot more, and have steady pay, for the amount of hours you put into being in sales.
I'm a personal trainer, who may as well be in sales doing what i do...I love my job for the most part, it's a passion of mine, I believe in the product I sell with all my heart, and I can provide dozens of personal references who say training with me is money well spent. It's still TOUGH to make ends meat doing what I do, I couldn't imagine slinging used cars that I don't have the some belief behind.