Fit and finish are two indications of a Mustang's structural integrity. Even an old beater that has never been restored will have good fit if it hasn't been wrecked or victimized by rust. Rusted-out framerails and rocker panels, for example, will adversely affect fit. Accident damage, even if corrected by a body shop, sometimes leaves body panels with a sloppy fit. Check door, fender, hood, and decklid gaps to see how they all fit together.