A、If the complaint is justified, you have to admit it readily, express your regret and promise to put matters right.
B、If the complaint is not justified, point this out politely and in an agreeable manner.
C、If you cannot deal with a complaint promptly, acknowledge it at once. Explain that you are looking into it and that you will send a full reply later.
D、All complaints should be treated as unimportant matters.