It's someone's job to know. I knew a buyer at a major office supply company. The buyers' responsibilities included occasional visits to the factories where suppliers made the products that were bought and then put on sale in the stores. This particular company had standards that they held suppliers to. When a buyer found workers at a factory with duct tape on their mouths, people living in squalor in the "dormitories", child labor or any other nonsense it was not uncommon for those suppliers to be thrown out of the store if it was not corrected. This was for a few million dollars worth of back to school supplies.

There's no way someone enters into a multi-year, multi-million dollar contract for high end electronics without ever visiting the factory and knowing what goes on there. They know damn well what kind of conditions exist and chose to do business with the supplier anyway. If they didn't know then they're too stupid to have their job.

They absolutely know.

I awarded a Chinese factory with a low five figures contract and I know exactly how everything is processed and made. For billions of dollars or purchase orders, I am pretty sure you can expect at least the same level of service.