You see an "iPhone 14 Pro" for $400. The seller says it’s "like new." Before meeting, ask for a screenshot of (blurring the Apple ID email, but showing the serial number). Run the serial through Apple’s site. If it shows "iPhone 13 Pro Max" or "Invalid," you walk away. If valid, also run it through Chipmunk to check Activation Lock. If locked, do not buy.
For that extra data, you need third-party tools. apple serial number search
You can find your serial number in several places, depending on whether your device is working, broken, or not even in your possession. On Your Device (Software) If your device turns on, this is the easiest method. You see an "iPhone 14 Pro" for $400
On a paired iPhone/iPad, go to Settings > Bluetooth , then tap the More Info (i) button next to your AirPods. If it shows "iPhone 13 Pro Max" or "Invalid," you walk away