Admittedly, the quality of a product helps business growth, and most good services got customers from the word of mouth. I mean, people referring others to go check it out, and that's actually the best form of marketing. Hence, making sure that whoever purchases the product talks to their friend about it, is the strength of quality products.
Discussions carried out by buyers with their friends about themselves who have experienced certain products are one of the marketing outside the company, but this is a positive value, because with customers who tell how good the products they buy are, this will be one of the quite effective marketing.
Besides, marketing relies on 'trust' to convert a prospect, and years of friendship is enough to tell who worths our money. Products like Coca-cola benefits from the "word of mouth" kind of marketing, because they've developed great relationship between their consumers and never failed in delivering quality soft drinks.
Yesterday, a friend told the husband that she feels happy drinking Coke...think of what the man would do when next his Wife is moody, he'd run over to the next store and get the product that makes her smile. Remember, the company didn't spend a dime, that was free marketing from a satisfied customer.