Our company is currently hiring for a position and we have interviewed half a dozen applicants. We decided to further pursue just two of them and call the references they had listed on their resumes.
One of the applicants, let's call him John, had two references. I called both and the first (his previous job) spoke highly of him while the second was surprisingly negative in their assessment of his previous performance. I have never encountered an outright negative reference before (usually, if a reference has anything unflattering to say, it's mixed in-between many positive statements), and I would assume that John is not aware this particular reference has few good things to say about him. We have ultimately decided to hire the other candidate, not John, primarily due to factors outside his reference, though the negative reference also played a part.
However, I was wondering whether it would be appropriate to warn John of his rogue reference? From our interview, and from his other positive reference, John seems like an excellent guy who would work hard, so it's hard to say why this other reference speaks poorly of him. Is it ethical and appropriate for me to, when I call him to inform him we will not be offering him the position, mention the negative reference so he can change it for future job applications? Or should what the reference said remain confidential? I would not divulge specifics.
The reference did not ask me to keep the conversation confidential or give permission to share, nor did I mention anything relating to that.