Short story: the smartest smuggler in history

Belgian national consistently for 20 years to cross the border on a daily basis about Germany on his bicycle carrying a backpack filled with dust. 

The men of the German border sure he "smuggled" something but every time do not find him is the dirt (!). 

The real secret not revealed until after the death of Mr. Dastanhan found in his memoirs the following sentence: "My wife did not even know that I built my fortune on bikes smuggling to Germany!". 

The element of intelligence here is (a red herring and convert Onzarnas goal for real!).