One of the most important things to look for is RUST. Check the trunk, floors and sides – if you can see through these, or they are severely rotted away you may want to pass. Quarter panels are easy enough to replace, but to fix the rest will be very costly. You might be better off spending more on the original sale for a car in better shape.
Matching numbers make a car more valuable. Check to see if the engine, transmission, and rear axle link up to the vehicle's VIN number. Most motors have the last six digits of the VIN number stamped on them, so they are easy to check. The transmission and rear end are a bit trickier. They are usually stamped with a date code, which you can look up to determine if the dates correspond. The fewer miles on the speedometer, the more the car is worth. But as long as a car is well maintained, you shouldn’t worry too much about it, especially on a restored car where many of the parts have been replaced or a Rest Mod that has been upgraded with current technology.
Some models have a lower production number than others. Those that produced smaller quantities have higher value than those that were massed produced. Basically, the rarer the model the better. Only 121,538 64.5 Mustangs were produced (and even fewer, 28,883, were convertibles) compared to say 294,160 ‘64 Chevrolet Chevelles, making the Mustang more valuable.
Big Block engines, which have bigger cubic inches and more horse power, are worth more than a Classic Muscle Car housing a small block. Though the gas mileage isn’t great, they were manufactured less than the smaller-size motors.
And the most important thing – buy a car you love.