Negotiating price with other men, who will almost invariably demand more money out of a woman than they would dare with a man.
That is a given. I was in the car business for over 20 years and always enjoyed a woman who knew how to negotiate, they are rare but they are out there. My mother was and still is antique dealer so I came by it honest.
Always watch closely body shops and service depts. that is who nails women the worst in the car business.