Treat Criticism and Complaints as Defects
If you have a customer who complains about something, don’t ignore it, no matter how crazy you think the complaint may be. If it can happen once, it can happen again; and more importantly, how many times has it already happened and nobody brought it up?
Of course not all criticism is valid, but you don’t know if it’s valid if you don’t take it seriously. Investigate every claim. Find the root cause of the complaint just as you would find the cause of a software defect. And once you’ve found it, see changes you could make, or what systems you could put in place to either stop it from happening, or mitigate the damage it could do.
If you treat every complaint as a defect, you’ll have fewer and fewer complaints over time. In addition, there’s simply nothing better than good customer service to promote word of mouth marketing.
[From my blog.]