Not a fool proof way, but when you buy, say, a $10 000 car, you should budget some thousands for repairs. Then if it breaks down soon after and it's too expensive to repair, your downside is $10 000, which is how much your $40 000 new car would depreciate in a very short time. If you don't have especially bad luck, this doesn't happen for every second hand car you own, but the depreciation is guaranteed to happen for every new car.