I want to apply for a car salesman position at a nearby dealer but they seem a bit shady?

Most dealers only offer a draw against the commission you will earn, not a salary or training bonus. If you do not make many sales or quit before you have paid the draw back you will owe them. Turnover is a good indication of poor sales opportunities or their bad selection of sales personnel. It is not a good job for most people due to the long hours with a lot of standing around.

Turnover is high because the hours are long, the success rate is low, morale is low, pressure and competition is high, respect is low, and some people's moral ethics won't allow them to do the things required to compete. It's a job for a unique kind of person. Most people who try find that they are not that kind of person. Hence the high turnover rate.