How do you identify subject-matter-expert commenters in a thread?

Identifying genuine expertise in anonymous comment sections requires reading for quality signals rather than identity verification. The most reliable indicator is the internal coherence of someone's claims — an expert response handles nuance, acknowledges limitations, distinguishes what is known from what is assumed, and does not overstate certainty. Responses that are confident about everything, that never say "this varies" or "consult a professional for your specific situation," are often more a mark of confident generalism than of genuine expertise. Commenters who provide specific, checkable details are more credible than those who speak in generalities. Someone describing a medical condition who provides precise mechanism explanations, drug names, or differential diagnosis considerations demonstrates knowledge that is harder to fake than a broad summary. That said, specificity can also be fabricated by someone who has spent an afternoon reading Wikipedia, so corroboration matters. Comment history is a useful tool when you want to evaluate a specific user more thoroughly. Navigating to their profile and looking at their posting and commenting patterns across time can reveal whether their claimed expertise is consistent with the rest of their activity. Someone who identifies as a software engineer in one thread but consistently posts irrelevant or confused things about programming in other threads is worth treating skeptically. Communities like r/IAmA and r/AskScience require verification from moderators before users can answer as experts, which provides a layer of credibility not present in unmoderated spaces. In other communities, look for user flairs that indicate professional affiliation (some subreddits grant these after verification), and weight peer responses — if multiple high-karma community members are deferring to a specific commenter or corroborating their claims, that is a meaningful signal of credibility even in the absence of formal credentials.