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GaKaye said:
If it's not printed on the menu, but is on the bill, then you're being taken advantage of as an American who doesn't know better.

This is the key. Moreover, I have seen bills where it says "tip not included." Another attempt to take advantage of the ill informed. As mentioned above, "tip" and "service" are one and the same. Of course no "tip" is included when "service" has already been included!