If you could spot one, you wouldn’t hire him would you?
All kidding aside. It is the classic points: Late for the interview but doesn’t apologize, inappropriately dressed, trashes prior bosses/companies, blames others for problems in prior jobs, never gives direct answers to questions, doesn’t look you in the eye, doesn’t have a clue about what your company’s business is, doesn’t ask you any intelligent questions, favorite words are “like, totally, whatever and umm.”
Ask your receptionist what impression the candidate made when he/she arrived and was waiting to see you.
HJG on The TPE Blog “Spotting Bad Employees Before Hiring”