How do start a letter of complaint?

The first thing to know about a letter of complaint is that, if you hope to get a prompt or satisfactory response, it is important that you present your complaint in a professional manner.

You may be angry, you may think their product or service is a pile of crap, you may believe that the company or the staff are a bunch of jerks, you may believe that you've been robbed; tell it to your family and friends, do not say it in the letter. Use your letter for the facts, just the facts and you will be more likely to get some satisfaction.

First paragraph, state the problem: I am writing to advise you that I am unsatisfied with the performance of your Zip Widget 2000. I have tried to discuss my problem with your customer service 800 number staff but have not had any success.

Second paragraph, describe the problem: Your advertising said, 'satisfaction guaranteed. Your 800 number people told me that the problem was my fault. But each time I attempted to use my Zip Widget, I followed the included instructions step by step and could not get the unit to operate effectively. In addition, the motor slowed down when even a small amount of pressure was applied. I can't tell if the unit is defective or that the instructions are inadequate. Bottom line, I am not satisfied.

Third paragraph, tell them what you want: I am enclosing the dated copy of my receipt for the purchase of the Zip Widget. Please send a refund for the total purchase price (including taxes), or a certificate to return the unit to the place of purchase for a complete refund, to the address printed at the top of this page. If you have any questions regarding this matter, you may call me at 123-456-7890. Thank you for your prompt attention to my request.

Sincerely,

It's important to tell them what you want or what you expect them to do, don't leave them guessing. They might guess that they need to do nothing, that you're just advising them. Keep the letter short and to the point so that your message doesn't get lost in a mountain of Words. That's all you need.