Measure to see that things are within tolerance, like ride height, and wheelbase and put it on scales to see if numbers are where they should be without things being over-adjusted.
Look for cracks around gussets and bent lollypops where radius rods attach to the chassis.
Look for bent radius rods, A-arms, and panhard bar, as well as rod ends.
Put the car on blocks, supporting the rear axle and put it in gear with the engine on so you can see if axles and/or wheels are bent.
Bleed the brakes...fluid should be clean.
Ask about oil change interval, number of races since rebuild, and ask for rebuild documentation.
Do a correct compression check. A good, sealed engine will be between 155 and 165 psi, and a unsealed engine cannot be more that 180 psi. 170 psi on an unsealed would be good.
Shake the drive shaft while looking at the U-joints. Movement is not good.
Pull on the top of the tire to see if there is any play in the rod ends and/or ball joints.
Anything outside these parameters is reason for price negotiation. There are other things to look at as well, but this is a good list to get you started at evaluating damage that may need to be fixed before, or soon after you begin racing.
