The color is often one of the first things that get noticed. There are very common colors like red, black, or white. Colors like Barbie Pink, Anaconda Green, or even Detonator Yellow may not be a great seller for a particular year. If the color seems to be a different shade from what you are used to, there’s a possibility that it could be something good.
The engine of the car also could help make the car even more collectible. There are cars that were made with a limited amount of a certain engine size. If the car does have one of these engines, it could drive up the value quite a bit.
Air conditioning is another feature to look for. The 1953 Chrysler Imperial was the first production vehicle in 12 years to get it after experiments with this feature that were made by Packard from 1939 to 1941 (it was discontinued because it took up half the trunk and was not very efficient).
Seat belts were only options that you could get if you wanted them when they first came about in the 1930’s. Another option to look for is power windows. Packard introduced power windows in 1941, and they were seen sporadically on cars and limos. It was decades later that they became common place in cars.
One feature that became standard (and even a necessity when there is a crash) are doors. There were some Model T cars that were sold without them (there were some model years, and even some of the higher priced models, were sold with them).
What kinds of classic cars have you seen that have something special?