OK, the problem with that is, if I am unhappy with the service, I should not be forced to wait for a manager to come over and remove the auto tip amount so I can put what I want in. What am I supposed to do, say to the waitperson, "hey, your service sucked, you ignored our empty soda and water glasses, you were standing in the corner talking to your friend, and it took forever for our food to get here, etc., etc. Will you please call the manager over here so I can tell him you did not keep our drinks filled, you were talking to your fellow waiters and our food was late, etc., etc, and have him take the 18% tip off so I can give you a 10% tip? Is that what I have to do now instead of just leaving a smaller tip when the bill comes?