The reply to a complaint should proceed from the axiom ‘The customer is always right’ and not from the antiquated policy of ‘caveat emptor’ (Buyer beware?).
No one normally makes a complaint for its own sake. All complaints should be treated as genuine complaints. A complaining customer is more deadly to the business interests of an organization than a rival company or a competitor.
If the customer is right, accept the complaint in the right spirit. Even if he is not correct thank the complainant for the letter. Regret the mistake or defect sincerely but not more than once. Unnecessary repetition of apologies and exaggerated expressions of regrets sound hollow and appear too soliciting. Do not go into great details about the causes. Do not shift the blame on to the quality of the raw material, workmen, quality control department and so on and so forth. Do not write as though you are doing a favour to the customer. These are days of consumer rights and do not appear to be doing a favour. Give in an assurance that such mistakes will not recur in future. If you are convinced that the customer is at fault, write your letter convincingly so that he reassesses the situation.