Establish Your Objective
The objective of a complaint letter is to prompt an action that resolves a conflict. You should avoid threats and accusations when providing the details of your complaint. Stick to the facts and your reader will comprehend what went wrong and what action you expect them to take.
In the first sentence of the sample complaint letter, the writer clearly states that he has received an incorrectly filled order, establishing legitimate grounds for both his complaint and request for corrective action.