In his book, Business by referral (and also here), Ivan Misner identified three levels of networking relationship, defined by their strength: visibility (V), credibility (C) and profitability (P). However he omitted any consideration of emotional intelligence. I have added the essential fourth stage: trustworthiness (T).
This is the weakest level of relationship. Each party is aware of the other, they will probably have observed each other and may have spoken briefly. However neither person knows much (or anything) about the other or their business. Although this would not seem to be a useful level of relationship, it is in fact essential—firstly, as a stepping stone to the later stages and, secondly, because it is too much effort to maintain every relationship in the later stages. So, although relationships at this level may not be productive, some effort has to be put into maintaining them.
Credibility has a chance of developing when each party understands what the other does; probably has some background knowledge about the other person; and certainly will have obtained other people’s views about the other person. In particular, each person will have demonstrated several times their competence and reliability to the other—whether by helping them or just showing up on time to a meeting. In other words, each party’s confidence in the other has grown.