Electronics vending machines show that Facebook trusts its employees to do the right thing.
But the Facebook system is different. No person controls the supplies of the small items. For example, they have nice Sennheiser headphones inside this vending machine. Any Facebook employee can simply walk up, swipe his or her ID card, and grab a new pair. There's a nominal price listed, but employees don't see that number debited from their paychecks or anywhere, really, outside of the IT vending machine. For them, it's simply swipe and go. The system trusts them to use their own judgment about what they need.