How would you interview someone you know well or someone you may even be friends with? What if you already know their strengths and weaknesses. I would prefer to avoid this situation by delegating this task to somebody else, but what if this is not an option. I feel like there is just too much personal feelings involved and it is almost impossible to be unbiased. If you have been in an similar situations, how did you handle them?
If you can't delegate to someone else entirely, involve other people in the interview. Make it clear to the person you're interviewing that you will be listening to other interviewers very carefully to make sure you make the best decision.
I think it can still be beneficial for you to be present at the interview. Observing a person's performance and behaviour will still be helpful even though you already know their strengths and weaknesses. You might notice something (either good or bad) you didn't pay attention to before, when you weren't critically looking at them as an interviewer.
Tell them someone else is doing the interview, but you're going to be sitting in. Then get someone else to come in and pretend to be the person in charge of the interview. You can give your fake interviewer a list of questions to ask, and still jump in yourself if you feel the need to.
Use whatever excuse you want to explain your presence, but make it clear that you will not be in charge of the interview and are not the person they need to impress to get the job. You could tell them its a training/learning exercise for you, or that you are there to access their technical skills since the interviewer isn't familiar with the language you're discussing.
It also gives you a convenient excuse if you decide to hire a different candidate.... just say you weren't the one in charge of making the final decision.
IMO this is not a big problem. Knowing the person very well IMO beats being unbiased. If the person fits the job well, hire him, otherwise politely explain that the job would not make him happy in the long run. Delegating that task to another person looks a bit like "I know too much too hire him, so let somebody else make this mistake".
It could only pose a problem if that person is very desperate, and you might feel forced to hire him even if he doesn't fit. But even in that case, it's more honest to tell him "sorry, I can't" instead of delegating this task to someone else.
Who is asking you to interview this person and why? Knowing that will tell you all you need to know.
For example, maybe this person is your neighbour, you have seen each other in the street and been at each other's house for dinner, but you don't know "how many years of C++ experience do you have?" or "have you ever written a Disaster Recovery Plan?". That is probably a pretty easy interview to run. "Look, we're friends, I already know you have integrity and you're smart, I just need to ask you some technical things."
A different example, this is your college buddy, you worked on assignments together, you know a great deal about the technical skills and personality traits that would be coming into the team, and you think this person is a definite hire. But management wants to cover their backsides and insists on an interview. Well in this case there is nothing you can ask that will change your opinion, so you should ask someone else to lead the interview.
If you must go through the interview yourself, and you feel it's not going to help you learn anything, schedule this person LAST. By the time you have interviewed 5 or 6 other people, it may occur to you there are things you don't know about what it would be like to have your buddy (spouse? cousin? child?) join you on the team, and you actually have some good questions to ask and a decision to make.
If I had to interview someone I knew well and couldn't get out of it, I'd probably try to set up a formal interview with some formal questions that are standard things like "why do you want this job" or "what do you like about this company" kind of basics where the key here is to see if something changes with this person. Some people may change when in an interview and this may be worth noting to some extent. There is also something about in this situation whether or not my friend rises to the occasion. For example, if answering the "why you want to work here" the answer given is, "Well, because you work here!" that wouldn't be very encouraging to my mind as I'd want to know how well do they see themselves in the job.
If I know this person well, then I'll already know whether they would be a fit for my workplace.
Sounds like you have a problem being honest with your friend. If you don't think they are qualified then tell them. Be sure to tell them exactly why. This is the only way to be a true friend. Give them pointers on how to be the type of person you need. It might be as simple as "we need X years of working with Y tech and it can't be learned on the job."
If it's more of a "I think you're lazy" type of thing then that's a whole other conversation, but one that you should still have if you are a true friend.
If you do think they are qualified then there shouldn't be an issue, just hire them.
I was in similar situation sometime back. I let other team lead take the interview. It is a weird situation and may end up being awkward situation for both of you. You may select the candidate or not it will have a guaranteed effect on your future harmony. As far as possible try to avoid or else you may be leading to turmoil
I was not hired by someone I know very well some years ago when I was pretty hard up for a job. He simply explained that the final decision was not his.
It stings a little more than a rejection from someone who doesn't know you, but for all I know my outspoken friend's boss just didn't want him having too many allies working at the company.
It's important, and it isn't.