For used cars, one that a lot of people don't think of is this one:

Find out if the engine has a timing belt or chain. If it's a belt, find out if it's been serviced yet since it can be an expensive maintenance item (sometimes it can even cost over $1000, depending on the car) and if not, when is it due to need it? Some people will sell their car right before it's due for the expensive maintenance tasks. You can at least use it as a negotiation point or factor it into your decision.

Most timing chains don't have a scheduled replacement interval, they're designed to last the lifetime of the engine though many get replaced when the guides start to fail.