By basing professional hiring decisions on candidates
While I am a senior linux engineer, I also contribute to the technical hiring of candidates. "professional hiring decisions on candidates" do not involve how technical someone is but how they fit into the team and organisation. There is no room for a double agent in a work place and those double agents are highly likely to be those who are antagonistic in their forum posts.
"Little prigs and three-quarter madmen may have the conceit that the laws of nature are constantly broken for their sakes." -- Friedrich Nietzsche