We all have contacts in the phone book and there are people we trust to, people who have connections to those who do something interesting. At the same time, our friends also have such connections in their contact books. And friends of our friends have. And so on...
If we get our friends, their friends, friends of their friends etc — we will have access to almost all possible goods and services we may need while having a big level of trust to those on the other side thanks to intermediaries we know personally and trust.