Bite your lip when a customer starts complaining about a repair, and you know she’s wrong. Instead, think of her as a balloon.
WHY? All you’ll do is argue back and forth. A better strategy is to just let the customer talk uninterrupted while visualizing her as a balloon slowly emptying of the hot gas inside.
HOW? When the balloon is empty, she'll be more responsive to what you would like to say.
SOURCE: David Geller