iPhone 7 shutting down randomly

A lot of things can cause the phone to randomly shutdown. Did the customer share any history of the device, such as previous repairs, drops or other impacts, cheap chargers etc.? I know you said randomly but have you or the customer been able to see any form of pattern, such as usage, apps, conditions or modules being used (camera etc.)? If it is truly random, it will be hard to figure out.

Start with a really thorough inspection with a microscope. Look for anything out of place or normal, such as traces of water (even if the LDI’s are good), dislodged or partially dislodged components. I like to nudge the coils as sometimes they are barely hanging on and can cause intermittent problems. Just don’t nudge too hard :>).