Judging sources

Who is telling you, and how do they know.

Method over authority

Expertise raises the odds a claim is right, and does not settle it. Ask how the person knows: did they measure, model, read, or hear it from someone else?

Check whether the expert is speaking within their own field.
Follow the citation. Chains of articles often lead back to one weak source.

Incentives

Ask who benefits if you believe it. Funding and motive do not make a claim false, but they tell you how hard to look for the weaknesses.