"In practice, I rarely reply to emails or GitHub issues, even if the sender sounds sincere. I've found that once you start being nice, some people will keep asking for more and then get angry when you don't keep volunteering your time.
Silence is the only scalable solution. I know that not making myself available feels unwelcoming and not inclusive; but I'm paid in my day job to serve students at my own university, not strangers on the internet who are using free software that I maintain in my spare time."
An interesting comment given past discussions on Hacker News about how demanding some users are about open source software (these users often tend to be other developers too).