How is the Yongnuo flash guaranteed? How about going to the factory or relying on boxes to ensure the whole country?

It's usually guaranteed by the store. Or after-sales, buy it and label it. Shops can also go after-sales with the three-guarantee certificate. In fact, the probability that this lamp is broken is very small. As long as it is not man-made or dropped, the average lamp can last for two years. Then you can buy a lamp after sale or change it online. It's easy to dismantle it yourself. It's not difficult.