Emotional complaints are usually the most difficult to handle, so these tips focus mainly on the more challenging complaints scenarios.
Aspects of Transactional Analysis theory are helpful in understanding and managing emotionally charged situations. Understanding where anger and upset come from and what triggers these emotions can help us to remain objective, and to separate the emotion from the actual content or facts of the matter. Transactional Analysis is a tremendously useful way to develop this understanding and the interpersonal (and self-awareness) capabilities which can be so helpful in handling difficult complaints and emotional people.
Many complaints are made by phone - in which case immediately take the person's phone number and explain you've done this in case the line is cut off, which helps pre-empt and diffuse a major cause of distress and frustration. Demonstrating that you have anticipated and guarded against this is a very positive first step, and this is especially helpful if the customer has been hanging on the phone, been transferred, or made previous attempts to resolve the problem.
If your policy permits giving your name and direct line then give both. In an age of anonymity, faceless voices, avoiding responsibility, and ridiculous impenetrable automated answerphone menu systems, when you demonstrate a swift firm clear personal responsibility for someone this is another big positive step.
If your policy permits it - which ideally it should do, although the policies of some large organizations prevent it - tell the customer that you will take care of the problem until it is resolved. This is your personal commitment to see it through. Even if you rely on others to fix it, the customer is seeking someone to look after them from start to finish. Customers failing to find anyone to accept personal responsibility for resolving their problem or complaint is a major cause of extra upset and frustration, so when a distressed customer finds someone who promises to take responsibility this lifts an enormous pressure.
Listen - let the other person talk and explain - and let them emotionally unload too if that's what they need to do.
When you listen, listen with feeling and empathy - the other person will be acutely sensitive to (and enraged further by) an automaton-like reaction, so try to really empathise on an individual and special basis.
When someone is very angry, exasperated or distressed, try to remember that they are feeling rather like a child does when upset and seeking reassurance or help from a parent or grown-up. They want to unload, and often just allowing people to do this will alleviate 90% of the problem, although do not ever expect any customers to admit to this. Think about your own experience when complaining emotionally about something - it is very difficult to remain angry and emotional much beyond a minute or two if the customer services person is really listening, allowing you to unburden, and understanding how you feel.
Do not confuse anger and rage on the other end of the line with adult behaviour - it is just another form of child-like tantrum or upset, and it needs absorbing calmly and sympathetically in an adult way. By your behaving calmly and being grown-up (which definitely does not mean acting officiously or patronisingly) the sooner the other person will be able to shift from 'child' or 'sergeant-major' back to sensible grown-up again. Again you might find the Transactional Analysis theory helpful in understanding how and why this happens.
Take notes. Get the facts. And take time and let it be known that you are doing so. This shows you are taking the problem seriously, that you value their words and their time spent explaining the problem. Also, by encouraging the other person to focus on the facts you can help to move the engagement away from emotion and into content and facts, which will normally reduce the stress for both of you.
Try to step back and look at the situation objectively with the other person, rather than getting drawn into confrontation or a head-to-head. Encourage the approach where you both work on the problem together to agree what should happen next. Keep control obviously, but involve the other person in your thinking and decision-making.
Understand how the other person feels. This is not the same as agreeing. It's important to show understanding. It is not possible to agree with an emotional interpretation or a mood, and until the facts are properly known it's not always possible to agree with even a perfectly balanced unemotional and reasonable claim or complaint unless or until you can substantiate the facts or claim. But you can always show that you understand how the other person feels, and this is a very big part of the customer's need at the time of complaining.
Of course if the complaint is plainly justified and clearly demonstrates a failing in your organization's service or product then you must acknowledge and apologise for the problem without dispute, and then focus on resolving and recovering the situation.
By understanding and being empathic about the other persons emotions they will often naturally extend you some leeway for a little firmness where required about your processes and the next steps. On occasions customer's expectations and demands are not realistic, which needs managing of course. The worst thing is to promise or agree to remedial actions or compensation that you will subsequently be unable to deliver. You will find it easier to be firm where you need to be if you have first shown a strong understanding of how the other person feels.
Rapport - trust - is necessary before you can move forward.
Here are examples of how to combine emotional understanding with control:
"Okay, I really understand and agree with you that this is very/unbelievably frustrating/annoying/stressful/upsetting/enraging to you, but for me to help you I must work within our processes, otherwise it'll be you and me on the outside trying to resolve this. My job is to find a solution for you and that's what I'll try to do if we can work together on this. Can we agree to go forward like that?"
If pressurised to agree or commit outside of what is reasonable or authorised you have to be firm and honest:
"That's not something that would or could be agreed at this stage if at all, I'm sorry. The customers who arrive at the best outcomes are those who allow us to work through our processes and consider the situation properly. I can't pre-judge it and I'm sure you wouldn't want to be dealing with me if I promised you something without knowing I could give it. If you let me help you with this I assure you that's the way to resolve this quickest and best. Can we go forward like that?"
Tell the customer what process or steps you will use to resolve the problem, which should always include a clear commitment to provide updates if appropriate, details of how decisions will be made, and how any remedial changes will be considered and incorporated into future procedures to prevent a recurrence. Many customers like to know that their complaint has been useful in helping the organization to improve its operations, and where this opportunity arises you should feed recommendations back internally and inform the customer accordingly.
Unless you are empowered to make exceptional arrangements you must work within your policies and systems. If you do not agree with your policies and systems then go through proper channels to recommend constructive changes, preferably supported with a brief business justification.
If your employer does not allow you to make recommendations then find another employer who will value your effort and commitment to the role. There are plenty of organizations out there who need all the good customer service people they can find.
In essence the professional customer service role is being an expert translator and mediator - a crucial pivot - in reconciling customer needs with organizational capabilities. At best the role will even influence organizational capabilities through good feedback and recommendations.
In keeping with such a role, you are a mediator, facilitator, and enabler. Remembering and aspiring to these qualities will help you do a great job and to keep an aura of calm and professional authority while doing so.