High turnover in sales has been common for forever in some dealerships. Many salesmen work only commission so they hire more than needed, don't train them and let anyone who doesn't meet quota go. Meeting quota is impossible because there are more salesmen than needed, and you need years to build up a following of loyal customers (most customers are not loyal no matter what you do, but the few who are go to the few long timers) . Non loyal customers like to think they are buying from the new salesman so long timers have a set of business cards without a name on them to hand out.

The above is what I remember from an Edmund's article from around 2000 when they hired a new writer and the first story was to get a job selling cars to find out what it was really like. I doubt much has changed. (Not all car sales are that way, but many are, and that is reflected in turnover)