In Norway, if you notice that the price at checkout is higher than what it said on the shelf, you can in most cases demand to pay the shelf price and the store has to honour it unless it is an obvious error such as some expensive electronics being tagged as costing an impossibly low amount.

It goes without saying however, that the customer himself is of course not allowed to alter the price on the shelf (like the Flipper Zero program in the featured link facilitates) and then pay the altered amount :P