Who is in charge of certifying *real* Christians?

Only God knows if you are a genuine Christian or not. There are Catholics that are very Christ-like and there are Catholics that are not. There are Baptists that are Christ-like and there are those that are not. There are Methodists that are very Christ-like and there are those that are not. You should not assume that anyone is a Christian because we might miss out on an opportunity to witness to someone who is good but is not a Christian. I hope this helps!