So - Watch For Rust:
When under the Hood, inspect the frame rails on both sides of the car. Look for rust where the frame rails meet the uni-body. Usually under the battery on the inner-fenderwell and on down to the frame rails. Over time, battery acid cleans the paint off the sheetmetal, and then it rusts completely though.
Look at the frame rails from within the wheel wells also. Make sure the metal is firm and strong. Knock on it with something strong and metal - make sure it isn't rusting from the inside out!
Bumpers: - Another area to inspect for RUST is the bumpers! Look behind them, they rust from the back side out through the chrome layer - so a very small hole in the chrome may mean an expensive bumper that is completely rusted out (and can't be fixed or rechromed later)
SO - Watch For Bad Rust Repairs Also:
Make sure you get the car up in the air, so you can completely inspect the undercarriage. Watch for bad or poorly done repairs, which have been covered up with "thick" undercoating. The stock factory undercoating was oversprayed with body color paint. Many dealers also applied undercoating prior to delivery, but these will for the most part look twenty years old. If you see fresh black tar based undercoats, beware...they are most likely covering up some problem.
Watch For Missing Parts:
Depending on your intended use of the car. You will want to assure that all the parts that you will need are there. If you plan to restore an older Z Car, you will want to make sure that all the original parts are still on the car (if they are not, you should pay less for the car, as you will have to find them, and pay for them!).
Major Items To Watch For Include:
ENGINE - Check to see if the car still has it's original engine. The original engine serial number is stamped both on a metal data tag under the hood, and on the block itself. Make sure they match. (if you plan on restoring the car to original, or if you plan to keep that option open for the future). Also check to see that all the original engine parts are still there - ie. AirCleaner, Emission Controls, Air Pumps etc. etc.
INTERIOR: - Check to see that the original seats are still in the car, and that the dash is not cracked. Make sure on the 1970 Models (as well as all others actually) that the car has the original gauges in the dash. This will give you a clue as to if the entire dash has been changed out. The '70 spedo started at 20mph rather then the usual "0"mph, and the oil pressure gauge went up to 140lbs....rather than the later models that went up to 120lbs.