What happens if I prepare with some guy from MBB and next week I go on the interview and he/she is the one to interview me? Can it backfire?
What does consulting firms think about this site
I will give you the info I got from managers from top consulting firms.
Either through internal referral or actually helping you with cases, two things can happen:
1) The consultant or the HR are aware of your previous relationship (this applies more for internal referrals) and decide not to use that particular consultant to interview you;
2) The consultant actually interviews you. The interviewer doesn't gain anything by allowing you to move to the next round if you don't meet the standards. Either he will look bad because you're going to bomb the next round after he recommended you, or you end up working for the firm but are a poor employee - either scenario goes against his own interest.
In conclusion, it can only backfire if you become too confident because you already met the interviewer before. Stay professional and do the case like you would do with any other interviewer.
Just my 2cents.