Over time I've learned to pay more attention to a sensation I think of as "Sneaking Suspicion."
Sneaking Suspicion is a "flavor" that some of my thoughts come with: it's a quiet little (metaphorical) voice that whispers "wait, but, are you sure?"
Lots of other voices in my head are much louder than Sneaking Suspicion. Sometimes I don't notice the whisper, even when in retrospect it had been whispering for years. But Sneaking Suspicion has a much, much better track record for honesty and correctness than most of those loud voices.
I notice that the people whose epistemics I trust the most appear to be extremely good at noticing their own analogues of Sneaking Suspicion. I think it's a skill similar to Noticing Confusion. But, at least for me, the term "confusion" doesn't really call to mind the right experience. It's not a "wha-- ???!" kind of feeling (Pikachu hurt itself in its confusion!). It's a lot more timid, and it has to be coaxed gently into speaking.