There are all sorts of people giving good explanations on almost any topic. Only some of them know what they're talking about. And there are plenty of experts who aren't very good at explaining, as they have spent their time and energy on gaining expertise.
So your heuristic easily leads to believing all sorts of nonsense. Antivaxxers, for example, frequently point to glib people with plausible-sounding explanations whose flaws are not at all obvious to the casual observer.
