How to know if “About This Mac” got modded and/or reset it I've seen plenty of articles about how its kinda easy to mod the "About this mac" section, however, I was wondering if I where to buy a mac from a stranger, what is a quick way to check the real specs and date of release without having to reset to factory settings.

It must be something quick so I can check it before paying for it without taking too much time.
Each Mac's serial number should be printed on the outside of the casing.


Locate the serial number. Apple provide instructions on how to locate the serial numbers on their devices here.
And then enter the serial number on Apple's Service and Support Coverage to find out the real model and age of the device.