He’s not complaining about the price tag not matching the online price. He’s complaining about the cashier applying the tag price and not the lower price advertised online. I also find it confusing when retailers apply different prices online and at physical stores, unless the fact that the online price is different is very clearly stated.
For some kinds of retail businesses I do expect one price independent of the location within the country. Not for groceries, of course, but I do expect consistent pricing in Zara or Ikea.
Few retailers selling sufficient quantities of high margin goods might do it, but most need to factor in local costs such as labor, property tax, and rent. Especially once the gap in costs diverge significantly between regions.