If any part in your car is wearing faster than the rest, eventually your whole car can break down.
Moving parts are always going to have the most wear and tear.
They move around a lot and therefore take much harder beatings than non moving parts, such as electrical circuits.This is true for both new and used parts, but I would highly recommend only buying used auto parts online if it is your only recourse.
Used parts can be very difficult to determine quality even with the product in hand, much less through someone's web page who is trying to sell it to you.Because very few are aware of vehicle auctions, many auto dealers are happy with that fact.
So if you are really intent on getting the automobile of your choice, shop for one now at salvage car auctions.Just like Duchamp used ready mades and called them art, such as his piece called the "Fountain" which was actually a used urinal, car parts and auto parts can be used as art ready mades.
Or take an old windshield and smear it with paint and you can be engaging in a type of performance art.