iPhone 13 Pro Max Oddities

Bought a used iPhone 13 Pro Max. There wasn't a single mistake on it. I used the phone for 4 days, after which the connection disappeared, the modem number was shown. I took the phone to the service center and paid $100 for the repair. After the repair, the phone started having problems with the camera, it was cracking, after which the application closed. У меня дома был iphone 13 pro с ошибкой камеры, я перекинул камеры между этими двумя телефонами и оба телефона написали что камеры подлинные и работают. I had an iPhone 13 pro with a camera error at home, I transferred the cameras between these two phones and both phones wrote that the cameras are genuine and work. But at the same time, the 13 Pro Max lost connection and gave an error, this time the modem number was gone. What's wrong with the 13 Pro Max? Why does it constantly lose connection?