It's especially difficult because there is actually good advice mixed with the bad and unsubstantiated. I've taken good advice from certain comments (e.g. that led to the discovery of open courseware and actually quality resources on physical exercise programs).
But part of maturity is learning to be skeptical of advice independent of upvotes, so one can get the good advice while avoiding getting mislead. To answer quick questions, I try to search for articles from reputable newspapers first (to see if a verified expert interviewed by a journalist is quoted at length) and possibly HN's archives via Googling with site:news.ycombinator.com. For more complex questions and topics, I try to find book recommendations from Reddit that were written by academics or low-profile experts over influencers, and then reading about the topic at length (e.g. it's usually far better to learn about big social problems if curious through well-sourced books, versus any hot takes online, regardless of the popularity of these hot takes).
you just failed your own test. "reputable" and "expert" indicate you're offloading evaluation to others rather than doing the hard work yourself of discerning the validity or plausibility of those claims.
I could study economics textbooks, take online courses, and get a part-time degree in economics over hundreds of hours, read economics papers from journals and the NBER (and equivalent institutions), develop a reputation and a network of experts, and then develop my own analysis and debate with these experts.
Alternatively, I could accept that I'm a non-expert for this particular domain, read some in-depth analyses in the Financial Times (a better source than Reddit), realize I should be cautious and save more, and move on with my life.
If the subject is more important, e.g. I want to work on a months-long project that requires an understanding of a specific economic concept, it would be useful to search for reputable books related to that topic and then study them.
don't look for experts, look for arguments you can verify through your own experience and validate through your own thought experiments. don't reach for immediate judgment, but rather, leave questions open until the evidence is conclusive. the term "expert" is rhetorical at best, and manipulative in most cases. relying on experts is a surefire way to be misled.
as a side note, there's an entire branch of marketing dedicated to using social proof manipulatively.
1) Successful people tend to be found in selective environments. A website that lets anyone in will by definition be filled with junk, bored people, teens, and time-wasters. Since 'successful people' know this, it's a self-fulfilling prophecy (they know their peers aren't there).
2) Most professional peer connections are still offline. Want to know what your peers think about a recent paper? If you're established in your field you'll know them on a first-name basis and will just call them.
Twitter is the only exeption to both these rules, miraculously, though only to a degree.