But if I were to say the service was terrible, and therefore I didn't tip, that would be disapproved of. In the US, I am expected to tip whether or not the serv

But if I were to say the service was terrible, and therefore I didn't tip, that would be disapproved of. In the US, I am expected to tip whether or not the service was good, so how does that incentivize good service - unless I'm expected to tip even more when I'm pleased with the service.