My brother and I inspected a car for a member on here last spring. We just put horse blinders on and looked at the car piece by piece.

Bring along some cardboard so you have something to lay on so you can look at the bottom for rust, patch panel work, etc.

Bring a flashlight, pen, paper, mirror, and a camera.

Use a mirror or stick your fingers up inside the tops of the wheel well lips to make sure the inner wheel wells aren't rusty, which usually means the quarter panels were once rusty too.

Look at the tail panel from inside the trunk for collision damage, and the bottom of the doors and trunk lid seams for rust separation.

If you stick your head in the trunk you can get a good view of the bottom of the rear window channel - a common rust spot on any old car.

Check the k-frame, frame rails, gas tank for dents or creases. Seen a few pretty clean looking old cars that were ran off the road, hit a tree stump or something like that some time in their life and the bottom of the car was never properly repaired.