I know all about shaved decks.
I have played in many gin games where they were being used.
I have stated in other "Illegal of the Day" posts, if I reconized what cheating device was being used, I sat down and said "Deal Me In." Advantage to Trimble!!!!!

My answer was what I thought the box maker was using it for.
It is quite possible the box maker was selling the device. If so, I may have handled one of his.

Someday I will relate the story of a gin game I had with a professer of mathematics. He was the head of math dept at the University of Cincinnati. Do I have to tell you Gin is mathematics?