How does Google actually know that a person that writes for a blog is an expert?

[Kross]

Expertise is one of the key things that Google uses to rank a blog or site. The more they perceive that a expert is the one that writes on a particular blog or site, they rank it higher.

How does Goggle discern that a blog is being owned or ran by an expert?

 

[Min George]

Google would try to trace the profile of the entity across the entire web to see if the entity is an expert. This includes social media posts, LinkedIn profile etc.