We are not called to judge but we are called to test the Spirits to see whether they be of God. Everyone claims to be of God in a Church setting, but there are usually a few false ones among the true believers so we need to be vigilante.
What i'm trying to show you is that we cannot judge a persons sin as a way to decide if they are saved or not. We have to follow the Scripture. There is a lot more to testing the Spirits then just going by what people say, that is correct. You must discern whether they confess Christ with their actions also. Confessing Christ is in both word and deed.
The last thing we should ever do is say "oh, that person did some horrible sin so their is no way they are saved" because that is un-biblical. We all struggle with sinful flesh and we all mess up, some worse then others.
Jesus forgave ALL sins on the cross. So the question becomes are they saved? and how do we know? The answer is do they confess Christ?