If the owner claims the car was never rusty, just look for areas of repair. Look at where the hood hinges bolt on to the inner fenders - look for any bulging rust areas there. Look at the rear quarters from inside the trunk - look & feel for any seams where the quarter skins may have been overlapped & replaced. Then look closely at the door jambs for where the lip of the quarter overlaps there - LOOK FOR SPOT WELDS! Look at the rear wheel lips & look for two layers of metal - the outer wheelwell lip & the quarter skin lip - they should both be visible & there should be very visible spot welds. Also down low behind the rear wheels where the trunk extension lip is overlapped by the quarter skin - you should see both & very apparent factory spot welds. Whenever a body shop or restoration shop replaces quarters, they almost NEVER spot weld the panels together or even try to duplicate the spot welds, & most places will short-seam the quarters along the top sides & never into the sail panel areas like factory. EXCEPT for really great bodywork, everyone else does it half-ass. I can look at 500 cars with quarters replaced & there might be one or two with spot welds & done right.