Mph. That sort of thing is more a kind of distributed authority. Searching for a term here.
When you have a single named geologist making a statement about an Apollo sample (or even several Apollo samples), there is opening for numerous questions; is she being mis-quoted? Is she under the influence? Is it April 1st? Is she honest and well-skilled but made a specific mistake in this specific case?
The more general question would be, "Do her views concur with the general consensus among geologist?" And for that, one has to know other geologists, or know the field in general.
But the argument, "Do geologists (as a class) believe these samples are from the Moon?" removes all of these. Instead of checking to see if specific statements are in accord, you are asking if it is reasonable to believe a field contains sufficient internal checks and balances to keep itself honest.
I think of a gauge. Assuming I didn't buy some sort of Chinese knock-off, what I have purchased includes the assumption that the company that built it calibrated it according to a standard, and that standard is maintained by an organization that thinks about such standards and works to make them accurate and useful. Of course the one specific gauge I am holding might be out of trim. If what I am measuring is critical, I need to measure the gauge against some other standard first. But as a working assumption, if I pull a random one out of a random box, it is probably not telling me complete fiction about what I am trying to measure. And the reason I can believe this has little to do with the antecedents of that specific tool, but the environment that causes precision gauges to come to exist.
So, "Jay, who claims to be an engineer, says..." is not strong. "Jay, who claims to speak for engineers, claims other engineers agree," is not strong. But, "Jay, who makes no claims, points out that engineers as a class would have raised holy hell," is a strong statement.
(And of course I can't leave it there. I've run into a number of hoaxies and other conspiracy believers who don't accept the idea of a scientific or technical field. To them, it is all individuals doing as little as possible, concerned only with keeping their jobs and keeping their heads down, and who do nothing but parrot whatever the official word is. The idea of the constant policing and, yes, sniping that goes on in the sciences to keep them basically honest, the complexities of certification and classification and licensing and professional bodies that make a sort of equivalent in the technical fields, heck, the idea of the individual scientist or engineer as active and interested, is entirely foreign to them. It doesn't appear to match their personal work experience, so they discard it.)
