From your comment above:
"It’s not possible for a seller to know every single other seller’s price so I don’t see how anyone has a reasonable expectation to that in the first place."
So if the seller can't be expected to know their competitors prices how can the consumer be expected to keep track of all that information for all the products they buy? Additionally, sellers evaluate competitors' prices and compare them to their own all the time.
I never implied a consumer should be expected to keep track. Not having perfect knowledge of every transaction in the marketplace is a risk for all buyers and sellers. Holding a seller liable for another seller's price is ludicrous though. That's the buyer's job to do, by not giving business to a seller who isn't in line with the market (other sellers). No reason to get lawyers and courts and regulatory bodies involved.
So if the seller can't be expected to know their competitors prices how can the consumer be expected to keep track of all that information for all the products they buy? Additionally, sellers evaluate competitors' prices and compare them to their own all the time.