I can't cite details, but I believe that case law has settled this many times.. When a customer enters a commercial business, there are implied contracts that are enforceable.. I am thinking of restaurants first. I believe it is the responsibility of the goods and services provider to show prices accurately and honor them, and variations of that are well-understood in court. These kind of transactions are common for thousands of years in the West.

It's called "dollar tree" for a reason, historically prices were and are a dollar unless otherwise noted.