alt Hacker Newswe have one of those by our office and it's funny how every day it says sold out but there's never really anyone there.
one time we did walk up to it as a few unscrupulous looking guys were hanging out and we figured they're just waiting for a restock. I don't think those vending machines really do anything to prevent people from getting as much as they want.
The card vending machines are effectively rate limited, you need to wait to make a purchase. This is so one person can't empty the entire machine, even if they have multiple payment methods.