This is a great post on social media and how trust is built through word of mouth and social networking. The image below is from the posting and I encourage you to go take a look.
“Trust in other people is established on the basis of promises kept. Either explicitly or implicitly we judge that a particular person is reliable, based on our own experiences or those of others. We don’t trust everyone we encounter of course, but a small number of those people we trust and who we happen to like will become friends; especially if the trust and attraction is reciprocated.” (From the posting). GO HERE TO READ IT.