When you hire a garage door installation worker or garage door repair person, you expect a certain quality of service from them, to reassure you that you will be satisfied with the end product, that you will get the price you want, and that you will be pleased with the customer service you receive.
Service people know (or aught to know) that many studies show that it costs more to get a new customer than to hold on to an old customer, and that bad experience leads to attrition of customers.
If a client is upset with an occurrence during the course of a garage door repair, a professional does not get emotional back, but keeps things in the realm of facts and figures. If a customer is angry, it is completely unprofessional to get angry back, and is legitimate grounds for complaint. If a professional is in a service-oriented field, they are trained to deal with these types of situations.
Half of the battle is establishing communication and understanding between all parties involved- if a problem is being related, the other person should repeat it back with different wording to be sure everyone is understanding one another. Then the main questions should be: "what can we do to resolve the situation?" "what could we have don't to prevent this?" and "I accept responsibility." (Okay the last one's not a question but it's important!)
Be sure to establish hand reiterate the agreed upon solution to make sure everyone's satisfied and the garage door comes out to everyone's delight.
In this way, service can be a breeze instead of a hassle.