I'm looking to purchase a used iPhone, but I'm concerned about the Find My iPhone security feature. I'm aware some people have trouble if this feature is not disabled, resulting in the phone not being usable by the buyer. I have asked the seller about this - they say the phone has been "factory reset". Is this enough to permit a new owner from using the phone uninhibited? Would they have had to explicitly 'turn off' the feature prior to factory resetting it? Thank you.