"Reliable source": Any source that has competence in the field of interest, without any biases or conflicts of interest related to the topic.
"Red flags" that will put me right off a source, is if they resort to buzzwords, name-calling, emotional language, or cutting down anyone who doesn't agree with their ideas. You won't find any of those on this website.
Finding reliable sources: What is a reliable source? University of Georgia https://guides.libs.uga.edu/reliability [retr 28 may 2022] How to evaluate the credibility of a source wikiHow https://www.wikihow.com/Evaluate-the-Credibility-of-a-Source [23 mar 2020; retr 28 may 2022] What are reliable sources? Bitesize - BBC With video, and links to info about spotting "fake news". https://www.bbc.co.uk/bitesize/articles/zdxj96f [retr 28 may 2022]
We will always be influenced by our past, by others, by preconceived ideas, our emotions. But we can try to take in information clearly and critically