As someone who self-studies science as a hobby rather than a career (read as: doesn't study science from any reputable institution and relies heavily on both the internet and books from libraries with various sources), how do professionals know that the people they're talking to / reading about are credible / know their shit? What sort of metric would be an acceptable use of measurement and how would I be able to test this metric out on my own? I can't imagine someone with a PhD or a Masters in Engineering would give out an exam just to see if a friend of a friend knows certain concepts.
Also, people writing PhDs and Theses would probably be doing the exact same thing I'm doing just with fancy certificates, background education, and institutionalized supervision / co-authors (if any) with the drawback of deadlines and a final paper, so is there any actual difference with regards to how professionals see people like me?