You'd be surprised. I worked at a movie theater, and most of the people who had "declined" cards would pitch a fit as soon as I told them that the card was declined. They'd claim that there's money on it or that I was "holding it wrong," but it's almost always out of insufficient funds. They also claim that punching in the numbers manually would work. From time to time, though, I'd get a card that was horribly mangled and unfit to scan, but those usually do just fine by punching it in manually and without a "decline" message. In the end, it all comes down to the customer being embarrassed about their spending habits, especially when they're at a movie theater buying fifty bucks worth of candy and popcorn.

You've obviously never worked in retail. I worked at Walmart for two years and I HATED having to tell people their card was declined. "Oh but I'm sure I have the money on there!" And then there are some people who are so paranoid about their cards that they wouldn't even let me try to help by swiping it on my end of the register. Good thing is, after 3 tries, the register locks up and won't let them try again. Since I didn't work a main register, I was able to send people up front or to another counter in the store.