How to Buy a Refurbished iPhone Safely?

The safest option is Apple Certified Refurbished, which Apple says includes full functional testing, a one-year limited warranty, and (for refurbished iOS devices) a new battery and outer shell.

Steps / Best Methods

Prefer Apple Certified Refurbished (direct from Apple) for the clearest quality and warranty terms.
If buying used elsewhere, verify the device is not Activation Locked (ask the seller to fully sign out and erase).
Check battery health, screen/camera, Face ID/Touch ID, speakers/mics, and ports.
Use a payment method with buyer protection and keep a written record of the serial/IMEI.

Option	Pros	Cons
Apple Certified Refurbished	Tested, warranty, cleaned; new battery/outer shell (iOS devices)	Limited inventory, still not ‘new’
Carrier/retailer refurbished	May bundle deals	Quality/warranty varies
Peer-to-peer used	Cheapest	Highest fraud/lock risk