How to check if activation lock is on / off before purchasing an apple device
An iCloud-locked device is effectively a "brick" and cannot be bypassed legally.
Open the Phone app and dial *#06# to instantly display the IMEI number on the screen.
Use the Apple Check Coverage website. While primarily for warranty and AppleCare status, it confirms the device’s model and authenticity.
A "Clean" status means the device can be legally resold and easily set up by a new owner. How to Find Your Device's Serial Number