What specific action must be taken with iPhones that are being returned?

When returning iPhones, it is crucial to ensure that "Find My iPhone" is turned off. This feature is designed to help users locate their devices if they are lost or stolen. If the feature remains enabled during a return, it can lock the phone and prevent the new owner from activating it. Consequently, disabling "Find My iPhone" is an essential step to prepare the device for its next user, ensuring a smooth transition and allowing the new owner to set up the phone without any complications related to the previous owner's settings. This action is particularly important for maintaining the integrity of user data and privacy.