Differentiate letter of complaint and letter of adjustment?

A lette of complaint is that which you have any complaint about any thing.

There are two advantages to writing a complaint letter rather than talking about it. First, you feel better. And second, the person or organization causing the problem takes you much more seriously when you commit your thoughts to paper.

A letter of adjustment is a letter that is written in response to someone who has complained about a product or service that you have sold to them. Its main goal is to offer reparation for your actions (if warranted) and offer a short explanation for your actions.