Usually the advertised price must be honored, because it may have brought the customer to your store.

For prices displayed on the shelf-label inside the store the law is usually not that strict (YMMV), as a shop-owner can refuse sale on check-out (otherwise I could put a pricetag on e.g. a shopping-basket and the shop-owner would be legally required to sell me the basket...).

Besides, most shops I've seen (in Europe) already moved from Infrared communication to RF (NFC or proprietary), for centralized shelf-label management without handheld devices. So all this study (and the underlying reverse engineering of the IR-protocol) might do is probably accelerate the transition from IR to RF-based ESL...

In your country merchants are not obligated to honor fraudulently altered price displays.

Probably mostly dangerous for the user, or are people routinely writing their own price signs in the store and then "buying" it for less? Walking up to the lot at the car store and crossing out some zeros? Don't see how this would be any different.

I guess they can use the cameras to show you were tampering with the labels and call the police. Somewhat related xkcd https://xkcd.com/1494/

In which country?