What is not appropriate to include in a letter of complaint?

details about the purchase price, model, and serial number
details about why you were dissatisfied with the product or service
a proposed solution to the issue
threats notifying the recipient of action you will take if not satisfied

Hello!

It is not appropriate to include any threats in a letter of complaint. Although the person sending the letter of complaint is dissatisfied, it is not appropriate to notify the recipient of any threats. It is best to remain rational and reasonable when dealing with an unsatisfying product or service.

When writing a letter of complaint, it is necessary to add the purchase price, model, and serial number so that the recipient of your letter is aware of the product in which you are dissatisfied with. Providing feedback such as details on why you were dissatisfied with the product or service will help the recipient develop a solution to the problem. It may also be beneficial to propose your own solution, which can help the recipient develop solutions to future issues similar to your own.

I hope this is of help to you!