The restaurant should have paid the customers for making it appear as though their joint was busy.
20%....I would have told the server I couldn’t tip because that money went to the surcharge so take it up with management.
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Also, I stopped going to a local seafood restaurant because they started tacking on some weird charge.....when I caught it I deducted from the tip and have never gone back.
That's why many restaurants have happy hour menus -- at least where I live. They are basically paying people to fill seats that might otherwise remain empty.