How important is "word-of-mouth"? When you are treated well or mistreated/insulted you tell your friends don't you? Praise/condemnation?

You warn friends because you don't want them to experience crappy treatment. You  tell them when whomever  treated you well. How people are treated can make or break a business. Good public relations is priceless. It doesn't cost a dime. You just treat people well and benefit from it. Or you can insult them and suffer for it. Simple.