gutenberg discount 

Price tag swapping, placing a lower priced item's price tag on a more expensive item in order to purchase the expensive item at a cheaper price. Named for the Gutenberg printing press, the first printing press with moveable type. This is considered shoplifting and will be prosecuted as such if discovered.got

The sole reason to use self-checkout is to score a Gutenberg discount.

Abby: "How did you afford those steaks? They cost twice your food allowance."
Benny: "Swapped the price sticker with a manager's special, got myself a Gutenberg discount."

gutenberg discount by Terran Shaman December 7, 2018