Visible crew/equipment: As Hogan, Le Beau, Kinch, and Schultz talk at the car, the boom mic is reflected in the chrome and on the hood.
Revealing mistake: The bunk that is the entrance to the tunnels appears to be moving upward about a split second before Newkirk taps the hidden key to activate it.
Answer: It's a comedy, not a documentary.
stiiggy
Perhaps it was counterfeit. There are numerous episodes where they deal in counterfeit monies.