I do not know, perhaps a lifetime of living in this world is enough to harden any soul. When a very retired man, and his very retired wife came to the counter, they racked up a hundred or so dollars in purchases. They slipped me the good old Visa card. I put it though and got an interesting code returned to me. I'm pretty sure this is standard retail stuff, but the card returned a code, a message to the cashier that something isn't right on the purchase.
Different codes correspond with different messages obviously.
Maybe its over the limit, or stolen, or cancelled, or any number of other reasons. So, I did my job. I'd do it again if I had too. I kept the card, and took out the scissors, all the while explaining that while I had no idea what the exact nature of the problem was, the store, as a Visa partner, had to follow the rules set out for us. And bla bla bla, if they wanted to know more, they should contact the number on the back of their monthly statement.