Here's another one: what I call the layshadow heuristic: could an intelligent layperson produce passable, publishable work [1] in that field after a few days of self-study? It's named after the phenomenon in which someone with virtually no knowledge of the field sells the service of writing papers for others who don't want to do the work, and are never discovered, with their clients being granted degrees.

The heuristic works because passing it implies very low inferential distance and therefore very little knowledge accumulation.

[1] specifically, work that unsuspecting "experts" in the field cannot distinguish from that produced by "serious" researchers with real "experience" and "education" in that field.