TNTi

Not a mechanic nor mechanically inclined but my personal used car buying routine:

1). Check the CarFax, not a perfect resource but better than nothing

2). Take my time visually inspecting the car (usually the salesman gets bored and goes off to "take a call"). I visualize that I'm detailing the car and go over every square inch. At least you might catch a miss-aligned panel (minor accident) or curb rash. Open the hood, hatch, fuel filler door, etc. An obsessed previous owner will clean all these which means that possibly he was just as obsessed with the maintenance.

3). Check the tires. The OEM's wear out ridiculously fast (IMHO) but shredded side tread will tell you that some expensive fun was had.

4). Look for an oil change reminder sticker. Might give you an idea when the last time the car was serviced.

A car at a good Nissan dealer or from CarMax is a safer bet because these places will generally perform some sort of multi-point inspection

Good luck with your purchase. Every Z I have bought has been used and they all turned out to be good, reliable cars.