As an Account Manager, it's part of your unwritten job description that you will have to handle a truckload of complaints over the course of your career. An Account Manager is the proverbial 'jam in the sandwich' between a client's expectations and situational reality, so when these two forces fail to meet (which is more often than we care to admit), you are the closest person your client has to: 1) vent to; and 2) seek resolution from. Knowing that you are guaranteed to experience snarky emails, heated phone calls, and tense meetings, it makes sense to learn how to handle the complaints when they land.
The first and most important thing to remember is that (even though it may surely sound like it) a client's complaint is very seldom a personal attack on you. Once you realise that you can take a deep breath, drop any defensive attitude and figure out how you will resolve the situation. You can't control how miserable your client may be acting, but you can control how you react!
The second most important thing to remember is that a complaint is your client giving you a chance to make things right. They care enough about your business relationship to complain. They could have easily kept quiet, turned their back on you and walked away - straight into the arms of another supplier.
"Treat every customer as if they have 10,000 Twitter followers." (Myers Barnes)
The third most important thing to remember is that a client's negative experience can spread like wildfire (if not handled appropriately), and can burn both your reputation and your bottom line.
A handy chart to remember:
Compliments tell you what you need to keep doing (or do more of)
Complaints tell you where you need to improve
Suggestions tell you how to improve
FAQs indicate needs that are not being met
Not all complaints are justified, and sometimes the client is just plain wrong. Though "the customer is always right" is not always a correct notion, a client complaint is usually valid to some degree, and it's important to remember that the issue is very real from your client's point of view. Even if they are wrong, don't overly concern yourself about being "right", as this type of response can sometimes get in the way of creating a great client experience.
Nobody likes dealing with complaints, but if you can take complaints in your stride, smile, and make everything right again in your client's world, you may be able to salvage a negative experience, and win your client over for life!