I have been to look at a car to buy, and noticed a rusty crack in the paintwork. It is a 03 fiesta, and the crack is on the outside of the wheel arch bit that you can only see by opening the rear door. It is in a large flat area, not near a seam or anything. the crack runs vertically, and is about 1.5 inches long.
What could have caused this crack to appear?
Bob