A car salesman was a salesman who sold automobiles during the 20th century on Earth. Individuals holding this position were often thought to be of low character.
In 1893, a time warped Data met a San Francisco bellboy who expressed interest in being a car salesman, assuming that Data would be willing to build them for him. (TNG: "Time's Arrow")
In 1947, Lieutenant General Denning of the United States Army Air Forces compared the behavior of Quark to that of his brother-in-law, a used car salesman. His tone was disparaging. (DS9: "Little Green Men")