One of the very best people we ever hired was so flustered in his final interview with us (a formality, after work-sample challenges) that he was visibly shaking during it. If we had taken the "numerous axes" on which the was "not a good sign" seriously, we'd have missed that hire --- and, I think, an entire business unit in our firm wouldn't have been started.
I generally think software developers (I count myself among them) know far, far less about psychological assessment than they think they do.
Of course that happens, but you're taking a real risk in hiring someone who can't get through the interview. I'd rather miss out on a good hire than make a bad one. You only have so many ways to determine whether or not someone is competent.
I don't know what to tell you. We switched to pure work-sample hiring and hired several dozen people that way. We retained all of them. I can't say that about our interview process prior to that: not only were we not picking up the "moneyball" candidates I'm talking about here, but we were also hiring people we (painfully) ended up having to let go.
I generally think software developers (I count myself among them) know far, far less about psychological assessment than they think they do.