Honestly I don’t acknowledge anyone as a “genuine” Christian because I don’t know what that is. It seems like you would need to have an unambiguous and complete definition of what it is and be able to read someone’s mind to determine if they truly satisfy the definition. Even if they declare they submit to the authority of the Bible, how do you know if they really do? Maybe you never see them in action when they don’t, but what does that prove?

How can you ever definitively tell if someone is genuine or faking? There will always be some doubt in your conclusion. This applies to all sorts of human categorizations, not just whether a person is a genuine Christian.