The epistemic spot checker could also notice flaws in reasoning; I think Rohin Shah has done this well.
Reasonably often (maybe once or twice a month?) I see fairly highly upvoted posts that I think are basically wrong in something like “how they are reasoning”, which I’ll call epistemics. In particular, I think these are cases where it is pretty clear that the argument is wrong, and that this determination can be made using only knowledge that the author probably had (so it is more about reasoning correctly given a base of knowledge).
The epistemic spot checker could also notice flaws in reasoning; I think Rohin Shah has done this well.