Explain the problem. Complaint Information.Please explain your complaint: Try to be brief, but be sure to tell WHAT happened, WHEN it happened and WHERE it happened. Take a look at this example complaint letter for ideas on how you should approach writing a letter of complaint. Complaint letters are like formal letters. They need to be written with no disrespect, and it needs to be done courteously. Consumer Action offers a sample complaint letter and an email complaint template. You can cut and paste these documents below. Find out how to craft a formal complaint letter. Learn about key components, structure, and tips for an effective complaint.