Beyond just being a "tech geek" hobby, checking a serial number on Apple’s Check Coverage page is your best defense in the second-hand market: Decode The Meaning Behind Your Apple Serial Number
If you are analyzing the serial numbers manually, here is the breakdown usually found in technical breakdowns: apple serial number check apple
You can find the serial number on almost any Apple device through the software or on the hardware itself: Go to Settings > General > About . Mac: Click the Apple menu () > About This Mac . Beyond just being a "tech geek" hobby, checking