Make Sure It’s Not Stolen
If everything else checks out, there’s still an additional step you definitely should take: you’ll want to make sure the device itself isn’t stolen. Even if the device is unsealed and in its box, there’s a chance that it could still be stolen.
For that, you can go to Settings > General > About and copy the IMEI (or MEID) number. Typically, it’s a 15-digit number attached to any smartphone. Once you have the IMEI number, you can paste or type it into the field into this CTIA Stolen Phone Checker website. (It may also be smart to see if the device is carrier-locked, which you can do with the IMEI number, too.)