Every lock in the game has a deterministic chance (based on object ID if a box and xyz coordinates if a door) of being unopenable by a credit card. Attempting gives the message “It doesn’t look like this lock can be opened with a credit card.”

• Boxes have a constant 60% chance of being like this, and doors are based on depth, starting at 10% or so on level 1 and increasing to 80% by level 50.
• Possibly extend this behavior to locks that can’t be opened by a key either, requiring either a lock pick or magic.