Just my opinion, but for me a used machine inspection is more about the overall feeling of the machine, and typically not something that is easy to quantify.
I've never, ever, seen a used CNC lathe that did not need a complete alignment of the headstock, turret, and tailstock. Just count on doing that. Even if it "makes good parts", count on an alignment.
Typically you are going to find a laundry list of other issues that the owner has simply learned to work around. Common examples: tool setter not working or not calibrated, way covers or wipers damaged, glass broken/cloudy, sheetmetal missing, safety interlocks missing or bypassed, problems with the chip conveyor, electrical cabinet looks like a family of squirrels have taken up residence, etc.
None of those things will stop the machine from actually working. Also, no inspection can predict the life of any electrical component. You may blow a spindle drive the day the machine arrives. That's just how it goes.
I've actually learned that I am not good at doing machine inspections because I'm in a position where even serious issues don't scare me.