When I worked retail in college, a declined card usually meant the user was overdrawn and overdue for payment. Certain codes in the system would require us to call the credit card company. I can remember on a few occasions we were told to destroy the card and not return it to the customer.
But yeah, mostly now a declined card just means you purchased something expensive or in a market area where you haven't ever spent significant money or is known to be a spot for theft purchases.