A book usually signals a quality higher than Medium signals.

Given the nature of the medium, books usually have the highest guarantee of quality due to the resources used to publish a book.

I usually search for documentation or tech problems in a text browser with cookies disabled, no js, no css, using tor and using an empty user agent.

I won't try to guess why, but the few pages I can access are always high quality, while poor quality pages (as discovered when opening the page anyway in a full browser) always try to block that setup.

You can usually tell from skimming the blog post / looking back at the author's history of posts - it's hard to put it into words.

I suspect quality means different things to different people and even changes based on context for the same person.

For instance, a blog describing some arcane linux command to run to fix the issue you're having does not need to be the same level of quality as something you're reading to learn + get in depth info about a topic you know at a very shallow level.

Sharing experts knowledge, not copying stackoverflow answer adding sentence from official docs and one screen long picture on top of the post.

Usually you can find the signal in the first 2 or 3 sentences of in any post.

Medium.com has better SEO than SO and small personal blogs, so it's winning when searching for a solution.

No single thing unfortunately. But as an example in contrast to Medium, articles published on github.io with simple HTML often seem to be a bit higher quality.

.edu