Reliable. The maintenance engineer will decide whether to replace some parts or a new machine for you according to the relevant public information and the situation of the mobile phone. Generally speaking, it is unlikely to replace a new machine. When returning to the factory for maintenance, first erase the iPhone, then sign the agreement. Finally, Apple will provide a backup machine that can be used during maintenance. If the agreement is signed, it can't be damaged, otherwise it will be compensated. After the maintenance is completed, take back the original machine with the standby equipment agreement and ID card.