100% depends upon the complaint, but good advice from Edward G - I go the extra mile whenever there is an issue or complaint. I deep dive the customers issue and try to resolve it for them in an efficient manner, making sure they are updated along the way to know that I am doing everything I can. There is nothing worse than making a complaint and then being ignored, it just angers people. Sympathize and put your self in their shoes
This really depends on what the complaint is, but first and foremost recognize the issue and sympathize with the customer. Make them feel heard and acknowledged while showing them your goal is to fix the issue. Sometimes that even means giving a refund and losing a customer. However, ignoring them to save a few bucks will anger them and could prompt them to spread bad reviews about you. Now one lost customer becomes 10 and your brand reputation is tarnished.
ThinkDiffusion