Here is a great example of how not to handle negative customer feedback (from The Consumerist via Stuff from Patti Shock):
A woman in Brisbane, Australia saw an ad for 50% off the bill at Casa Flamenco, a local restaurant, so she and some friends went out for dinner. The experience wasn't good—untrained waiter, mediocre food, small servings, long wait time, and despite the half-off coupon the meal was surprisingly expensive for the value. The woman—a restaurant marketer—wrote a polite email to the restaurant with some professional feedback and suggestions on how to improve service.
Here's what the restaurant wrote back to the woman:
your are an idiot we dont need your feedback.