Did you see that sign "Welcome to the United States" when arriving at the airport? That was the clear disclosure that from this point on, every restaurant price is [menu price] * 1.3. Just keep that in mind when ordering.
No, that sign is clear disclosure that you are being welcomed to the United States.
Even if we assume the person is familiar with American culture, it is only restaurants with wait service having prices times 1.3 (including sales tax).
That's nonsense. If that were true, not tipping in an American restaurant would give the owner the right to take me to small claims court to recover the missing tip. Do you really think simply stating that "everyone knows" would convince a judge to rule in the restaurant's favor?
