写作模式
说明投诉问题—>描述具体情况—>期待解决方案。第一段需写写信的目的;第二段阐述问题及后果;第三段给出具体的期望。
经典句式(投诉产品)
第一段需写写信的目的以及自己的一个概括的期望。
I venture to write to complain about ……+定语从句
I would be grateful if you could do anything necessary to solve the problem facing me.
第二段阐述两、三方面所面临的产品或服务的问题及后果。
there are several aspects underlying this complaint. 
For one thing,......For another,......In addition,......
第三段给出具体的期望,比如退款或更换新产品。
It is my sincere hope that you could give me full refund or replace it with a new one. Your kind reply to this letter at your earliest convenience would be very much appreciated.
范文
Dear Manager,
I venture to write to complain about the quality of the digital camera I bought last Friday at your store.
During the five days the camera has been in my possession, problems have emerged one after another. For one thing, the screen is always black, making the camera no different from a traditional one. For another, the battery is distressing as it supports the camera‘s operation for only two hours.
Therefore, I wish to exchange it for another camera or declare a refund. I will appreciate it if my problem receives due attention.
Yours, Li Ming