Problem of Being an Expert and Having Expertise

In a comment to the post Larry Sanger, Citizendium, and the Problem of Expertise by Clay Shirky, Eric Finchley wrote:

["You" here refers to Clay Shirky] I disagree with your comments on expertise. It seems to me that you are conflating expertise and authority. A judge has a socially constructed authority to pronounce sentence, just as an opinion commentator has the authority to write for a diverse audience in a national newspaper. But we haven't said anything about their expertise here.

Another example: cardiac surgery. Are you suggesting that the reason a cardiac surgeon is allowed to operate is entirely socially constructed? Surely such an individual has a fairly unique set of abilities, expertise, in this domain. The reason we don't allow Indian MDs to do this without review is to verify that such a person has the skills and knowledge to be operating successfully -- that is, that they are an expert. Now, those standards may be social facts, but in most cases they are reasonable and necessary.

David Berry also commented:

This is a very interesting argument but I think you overplay the socially constructed nature of authority and expertise and underplay the obduracy of expertise-reinforcing institutional outputs (such as PhD certificates etc). So, I agree that indeed they are social facts, but "expertise" is also manifested in concrete objects in the world which prescribe back on us a particular preferred social network organisation. In other words, experts are experts due to a network of human and non-human actants.

Is expertise pure "social-fact", a socially recognised procession of a collection of "scientific fact" as in positivism, or a connection of nodes including other experts, databases or organisations?