Have you ever heard of the halo effect ? It is a cognitive bias that makes us have a positive or negative opinion of a person based on the very little information we have when we meet them. We will use elements of his environments ( a group he belongs to, the way he looks and dresses, his acquaintances, etc.) to form an opinion about him.
It could be called the "first impression syndrom", if the first characteristic we associate with someone is positive, we will tend to judge everything about this person on a more positive note. The opposite works as well.
This is an important thing to keep in mind when you are networking as this "halo effect" seems to affect pretty much everyone. Pay attention to how you introduce yourself in professional contexts as the first impression might make a big difference.
This is also true for the way you show yourself online so do not forget to update your profile and pay attention to the way you communicate via private messages for example.
More about the halo effect :