The problem is that most people have no idea and no interest in their cars. They treat it like a washing machine or a gas boiler, just using it until some light or warning comes up, then they ask "is this red flashing light saying "Warp core breach! Stop the engine" anything to worry about? I've been driving it for like this for a few weeks hehe!"
The simplest test is just checking the coolant and oil levels. If they've never been topped up, or they're full of mud, then that's maybe not the best sign. Nor is an engine compartment full of last summer's dust and dead insects etc. .. although at least you can spot any oil leaks more easily.
Ralf S.