About 7 years ago I moved to one of the most affluent parts of the UK (outside of London) and had my mind blown when every item on the shelf in the tastefully decorated Morissons supermarket had e-ink displays for every item.
As an engineer my immediate thought was whether they update these on-the-fly with different prices depending on who walks in the door (they don't).
At least in Portugal, prices on a supermarket can only be lowered during the day, never increased. The logic is: During a dynamic price increase, a customer may pick an item from the display at the low price, only then to be charged the higher price at the register; the store would be found lying on the displayed price, which is illegal.
That's interesting. I worked in a supermarket as a student (in the UK) and was told when I asked (because I like to ask these sorts of questions) that here in the UK, the retailer is not obligated to honour the implied contract.
Essentially, if the price is wrong on the shelf, they can simply choose not to sell you the item if you refuse the correct price. In reality, larger stores won't want to upset a customer and generally will honour a lower price. It's more likely to happen when buying a loaf of bread than when buying a TV, or a car for example.
As an engineer my immediate thought was whether they update these on-the-fly with different prices depending on who walks in the door (they don't).