资料题：What is the main topic of the passage（　）。

Not every service or product meets your satisfaction.When you are dissatisfied, you should voice your dissatisfaction.One reason for doing so is to help the vendor know there is a problem.The problem may have been created at a lower level in the vendor's company, and the vendor himself may know nothing about it at all.You render him a service when you bring weaknesses orfailures to his attention.A second reason for writing a letter of complaint to a vendor is to seek redress.You may notwish to pursue the matter so far as to take legal action, but you may wish to give the vendor theopportunity of making good.Most vendors value your business and their reputation sufficiently to replace defective goods, resupply work that did not meet specifications, or refund money when necessary.No vendor likes to do B0, but your carefully worded letter of Complaint may motivate him to do so.When you write a letter of complaint, you' d better keep these TPS in mind: First, be courteous though firm.You will not win a vendor's cooperation by anger.Secondly, be reasonable.Show logically and factually that the responsibility lies with the vendor or his claims.The vendor should be impressed with your fairness and quiet grasp of the facts in the matter.Thirdly,be specific about what is wrong.Be equally specific about what you want done about it.Lastly,tell how you have been hurt or inconvenienced by the problem.This strengthens your argument for redress.