A tip needs to be for the part of service you can directly evaluate. If you give the same tip everywhere you are doing it wrong. If you don't stop think about it that is wrong. If paying for the group the tip is a group discussion even if the rest of the cost is kept secret.
A confounding factor is you don't generally know whether a server gets the tip. Many places create a pool of tips that gets distributed across the wait staff and sometimes even the rest of the staff.
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A tip needs to be for the part of service you can directly evaluate. If you give the same tip everywhere you are doing it wrong. If you don't stop think about it that is wrong. If paying for the group the tip is a group discussion even if the rest of the cost is kept secret.
Pay for value, the percent is a suggestion.
A confounding factor is you don't generally know whether a server gets the tip. Many places create a pool of tips that gets distributed across the wait staff and sometimes even the rest of the staff.
I consider that fraud. Though the law probably does not.