With NFC, they could just limit the list to devices in close proximity to the point of sale. That said iPhone doesn't have NFC so they need to solve that proble

With NFC, they could just limit the list to devices in close proximity to the point of sale. That said iPhone doesn't have NFC so they need to solve that problem some other way. The general point of scale issues still is valid, but culling the list of payers seems surmountable.