This was at a time when I was working as an ECA. A new ECA had joined and there were some issues at the site so he requested me to come to the site to sort things out. There the customer was in such an angry mood that I was scared that he may even ask us to leave the house and stop the work. But, it was nothing, I simply heard him out for some time and after 5 minutes the customer was completely normal after that. Whatever work was remaining we completed that and finished it.
So listening to the customer is very important, second is the way you are talking to him and third is cleanliness. When work is going on, the customer sees how much cleanliness you maintain in the house in the morning and evening. The customer is very attached to cleanliness.