[alkonaut]

I glance at their code to see if there is something that can say whether they are very good coders or terrible coders. Usually you can't say anything though.

Something I really try to find is how they communicate when writing bugs, responding to questions, differences in opinion etc. If you find someone who can respond to an angry user of their library because their feature wasn't implemented, or that can politely turn down a PR for example, that's really good sign.