This is a bit unethical, but the candidate in question could just say that their current employer gave them a newer, better offer that they couldn't refuse, ess

This is a bit unethical, but the candidate in question could just say that their current employer gave them a newer, better offer that they couldn't refuse, essentially giving plausible deniability. Though I do agree that the interviewer would be fully in their right to not re-interview the candidate.