The proprietor also had the opportunity to credit back the customer's money twice - having the wrong advertised prices on a menu is the proprietor's mistake. In the first response, the owner should have offered to credit back the $4 not just send an updated menu. This likely would have diffused the whole situation. And then on the second reply when asked for $12 he shouldn't have just offered $3 (not even the full amount). It's an antipattern for running a small business to not honor a lower price if an employee (or website) misquoted a lower price than is usual. And in most jurisdictions it is also illegal.