I hear this quite often about Github and it's a bit disturbing to me. If I heard an editor judge an author's work based on what that author posts to twitter, I'd be horrified.

I can't be the only person on Github that uses it primarily as a junk drawer full of bad implementations and abandoned "projects" that were more quick and dirty personal itches. Sometimes I'll contribute to random OSS, but the vast majority of GH for me is just a place to store random ideas, many of which were just toying around with some new tool or whatever and would never see the light of day in production without given much more thought.

Honestly, if you want to see code samples, you're probably better off watching the person work through a problem. Give prospective hires a project. Whether its as simple as fizzbuzz or as difficult as a trial week is up to you, I suppose.