"I've never seen anybody do anything to your food, but I have seen servers mess with your credit card. If a server doesn't like you, he might try to embarrass you in front of your business associate or date by bringing your credit card back and saying, 'Do you have another card? This one didn't go through'" (source).
"It's much easier to be recognized as a regular on Mondays, Tuesdays, or Wednesdays. Once you're recognized as a regular, good things start to happen. You'll find your wineglass gets filled without being put on your bill, or the chef might bring you a sample" (source).
"If you make a big fuss about sending your soup back because it's not hot enough, we like to take your spoon and run it under really hot water, so when you put the hot spoon in your mouth, you're going to get the impression---often the very painful impression---that your soup is indeed hot" (source).
"If you're having a disagreement over dinner and all of a sudden other servers come by to refill your water or clear your plates, or you notice a server slowly refilling the salt and pepper shakers at the table next to yours, assume that we're listening" (source).
"Use your waiter's name. When I say, 'Hi, my name is JR, and I'll be taking care of you,' it's great when you say, 'Hi, JR. How are you doing tonight?' Then, the next time you go in, ask for that waiter. He may not remember you, but if you requested him, he's going to give you really special service" (source).
"If you're having a problem, speak to the owner if you can. Managers may have very little power. They're less likely to compensate a meal, and most aren't authorized to give away free alcohol. They'll also take it out on the server if you have problems" (source).