I think a rule which says that once a price changes, the POS system must universally use the lower price for the next two hours (for the largest supermarkets, m

I think a rule which says that once a price changes, the POS system must universally use the lower price for the next two hours (for the largest supermarkets, maybe 1 hour for a mid-sized, and 30m for a small metro sized shop) would be appropriate. So, if a price increases it’s very unlikely a customer who has seen the lower price will be charged it, and if a price lowers, it must be implemented instantly.