Brinkmanship

This is a very short fiction story about a theoretical type of person who is a genius at selling cars because of his well-developed skills of analyzing potential buyers. He pushes buyers as far as he can into ordering a more expensive car with lots of extras, but he tries not to go beyond the "brink" where they will walk away becuase they feel they have been pushed too far. He has the ability to make buyers like him and follow most of his suggestions.