Check the IMEI
The IMEI is an important identification number you can find on your iPhone by going to Settings > General > About. This is a particularly important code because it’s commonly used to check if the iPhone is stolen or not – something you should always be aware of. Check the IMEI before you agree to purchase. Once you have it, you can go to Swappa or to StolenPhoneChecker and input the code to see if anyone has reported the iPhone stolen and had it blocked. You do not want a stolen phone, no matter what the seller may try to tell you. Some scammers may try to lie about the IMEI, but fortunately, this is rare (and you can check in person if possible).
Additionally, the IMEI can be used to check and see if the phone has any activation problems. Call up your phone service provider and provide the IMEI number to see if the phone can work on their service, or if it’s blocked. Some carriers block phones because of signs of trouble or incompatibility issues, so it’s important to check this out first.