Aaron - if a customer shows a shopkeeper a picture of a face that is not them, what happens if the shopkeeper is tired or hungover and can't distinguish up from

Aaron - if a customer shows a shopkeeper a picture of a face that is not them, what happens if the shopkeeper is tired or hungover and can't distinguish up from down? Or, the shop just needs the money? If I was managing a shop, I wouldn't want a hungover teenager "confirming faces." What am I missing here? The only person I'd want confirming faces are customs officials and police officers - where there's a clear need to show the right ID to such a person and a clear disincentive to show the wrong one. At the same time, the checker is compelled not to mess up. As a shopkeeper using facecash, what happens if myself or my staff mess up, is there a liability? Why would I want that liability? And if there's no liability, what's negating a potential fraud? What happens if there is a dispute between a customer and a shopkeeper as to the face in question?