Referred candidates may be a great fit for your position, but how do you know for sure? As an interviewer, it is easy to overlook weaknesses in a referred candidate because the “likeability factor” has set in deeply. Best practice is to evaluate referred candidates just like all other candidates. In fact, best to be even more thorough. If a hiring mistake is made, you certainly won’t enjoy telling your referral source that you fired his friend.
4 Best Practices:

Interview – Conduct formal office interviews and ask the same challenging questions you would of other candidates.
Assessments – Verify behavioral style and skills to ensure job fit.
Objective interview – Engage a professional interviewer to evaluate the candidate and provide an unbiased opinion. (Safari can help! Click here for more info.)
Reference Checks – Talk to at least three professional references, preferably past supervisors.