
From the day you open your doors as a business owner to the day you retire, there is bound to be someone you make unhappy. Your wife, your husband, your best friend, your kids, someone out there is going to disagree with you or be against an action you do. This is an unavoidable fact. What you do about it matters.

Tommy Mello writes in his book Home Service Millionaire his 5 steps to diffusing an angry customer and even turn them into a fan:
Every once in a while, you or your technician will have to deal with a customer who is angry about something. It may be that he thinks the previous technician did a lousy job, the garage door is defective, or you didn’t get there fast enough.
Here’s how to diffuse an angry customer and even turn them into a fan:

Be calm and polite:

When the person you’re talking to is tense, it’s imperative that you keep cool and calm from beginning to end. Getting angry with them will only cause the situation to escalate. If you need to, take a few minutes to breathe, walk away, and return when you can be calm.
Acknowledge their pain:
Show empathy by saying
“I’m sorry you are having these issues with your garage door. I’m here to help you.”
Let them vent:

The irate customer might go off on you and say something like
“This is all your fault! Your lousy company can’t seem to fix anything! This is the third time you’ve been out here, and I still have this same problem.”
It’s OK. Don’t take it personally. Keep being nice. This is the time for the client to vent, not you. Once you feel you have your customer’s attention, use the information from your observations to build what persuasion, compliance, and negotiation expert Dr. Robert Cialdini refers to as “connecting points.”
Let’s assume you’ve already looked around.
You noticed the electrical box in the garage was corroded and suspect the garage door motor isn’t getting consistent power.
You might say, “Sir, I noticed you have a corroded electrical box in the garage. Is it possible the garage door motor is not getting consistent power, which would make it work intermittently?”

Show the customer the old circuit box.
Chances are they’ll say something like, “I saw that and was thinking about calling an electrician.”
Focus on creating solutions:
Having endured the customer’s tirade, it would be easy to rub this obvious defect in his face. That would also be a mistake—if your company was involved with the garage door previously, your technician may have missed this problem too.

What your customer needs is a SOLUTION, NOT EXCUSES or explanations.
You can be right but still not win! Being right is all some technicians care about. They need to understand winning is what really matters.
Gently educate the customer.
APOLOGIZE for not noticing the underlying problem and SUGGEST A SOLUTION.
If the problem was caused by a technician from your company, apologize profusely.
If you’re a company owner, your service technicians must have the confidence and ability to call you and get an immediate decision on whether to offer the irate customer a special deal or free service.
Nothing makes a wronged customer happier faster than to have the problem fixed at NO CHARGE!
Always look toward the future:

When you start any service call, it should be with the future in mind.
You should ask yourself, “What will it take for this customer to be loyal and stay with us?” Most people are ready to forgive and forget, but only if they’re treated with respect and courtesy and their problems are solved quickly
This problem WILL HAPPEN at some point throughout your career. How you handle the situation, however, makes all of the difference.
A Forbes online article also offers some further advise:
Do not take it personally:
The customer is not initially angry with you. You may not have ever visited their residence, spoken to them, or even hear of the problem before this meeting. They are angry, do not take that to heart.
Use your BEST listening skills:

Listening patiently can make all of the difference. Tommy stated above to let the customer vent. Listen to them, hear what they are really saying. Do not jump to the defensive, rather listen for the root of the anger. They may have called because their garage door is faulty, but is that what is really causing the anger? Were they just having a bad day, one problem right after another and this was the straw that broke the camel’s back?
Your body language is also important. Keep eye contact, stand or sit straight, keep your arms uncrossed, etc.
Take a personal “time-out”
When you work in the home service industry, or any industry for that matter, your work is not going to be perfect 100% of the time. Yes, your goal is to come as close to that 100% as possible, but in reality, what you do when you fall short may be more important to your company that the idea of being perfect.

“The most valuable thing you can make is a mistake- you can’t learn anything from being perfect.” –
Adam Osborne