To whom it may concern,
I am delighted to learn that 题干交代的背景. And I am writing this letter to express my suggestions on 话题.
To begin with, I would like to suggest 建议内容一（that+包含should的句子）. In addition, It is necessary / beneficial for you to 建议内容二.Terminally, you’re supposed to 建议内容三 ，which is a good way to improve .
I would appreciate it a lot if these suggestions are seriously taken into consideration. Thank you for your time and attention to this letter.
Yours sincerely,Li Ming
I am写信人身份. I am writing this letter to express my dissatisfaction / complaint to you.
I bought a/an________from your on-line store last month, but I found that there are some problems with it.（描述事实） Firstly,________, which is the main reason of my dissatisfaction. Secondly, ________.This is another problem. All in all, there is still much room for improvement. Before I take any further action, I do hope表达本人的愿望. / I would like to exchange it for another one or get a refund/compensation.(提出赔偿方案）
Considering this situation, it would be highly appreciated if you could take my letter into serious consideration. I am looking forward to your reply at your earliest convenience.