Look down the sides, not at them
Stand at the front corner of the car and sight down the side at a low angle, then do the same from the back. Original factory panels reflect light in one continuous line. A repainted or straightened panel shows up as a ripple in that reflection, even when the color match is perfect. Do it in daylight; showroom lights hide a lot.
Panel gaps and the way doors close
The gaps between hood, fenders, doors, and trunk should be even along their length and match side to side. A gap that is tight at one end and wide at the other usually means a panel was replaced or a structure was pulled back into shape. Open and close every door, the hood, and the trunk. A door that needs a push to latch, or a hood that sits a little high on one side, is worth a question.
Paint texture, tape lines, and overspray
Factory paint has a fine, even texture. A resprayed panel often has a slightly different orange-peel pattern, and the edges tell the truth: look inside the door jambs, under the hood edges, around the rubber seals, and on the black plastic trim. Overspray on a seal or a trim piece, or a faint tape line, means paint work. None of this is automatically a problem; a well-repaired fender is fine. The problem is a repair nobody mentioned.
Bolts, welds, and the underside
Open the hood and look at the bolts that hold the fenders. Factory bolts have untouched paint on their heads; a bolt with chipped or wrenched paint has been removed. Check for fresh undercoating sprayed over one area only, which can hide a repair or rust. Then compare what you found with the Carfax: the car and the report should tell the same story. If they do not, that is the car to pass on. Every car on our lot went through this before it was listed, and I am happy to walk any of them with you.