Did he show you that new Imperial in another color? The seats look like they have been recolored with lots of red paint and they will need immediate attention to avoid the leather ripping apart, but they appear original and saveable. The underside also looks alright, not covered in fresh underseal to cover up rust etc. That underside crack looks like it is supposed to be there.
But,
have you checked the areas around headlights, lower fenders and rocker panels for excessive use of plastic filler? A gauge for that is not too expensive. If you can borrow a endoscope and look into the inner wheelarches that would also be good. Have you tried driving it, does it steer straight and does the brakes pull up straight? Is there excessive smoke for the engine, is it hard to start cold or hot, does the engine temperature and oil pressure at idle stay normal?