Why 'once saved always saved' could actually be correct

There is always a big discussion/arguement going on between the osas proponents and perseverence people. I've been thinking. The term "Once saved always saved" could actually be correct. It is a long stretch to get to it but deep down it may be correct. The way I see it is this; How does a person know when they are really truly saved? And do we really really know? The Bible says to confess and believe in our hearts... But can another person really know when someone else is saved or not? I would think it is quite impossible for the simple reason that we cannot know somone elses mind or heart. And do we really know our own, for that matter? Could we be included in the "Be careful if you think you are standing firm...." Warning. Why would we have to be careful unless we could fall. I think that falling isn't always from a saved position.. it could be from another place.. such as a 'standing firm' or think we are standing firm place. The problem I have with osas is how many pastors present it. They present it in a way that makes it 'ok' to sin now. Once you confess with your mouth in public and pray the prayer. You then are able to do whatever you want, no matter how bad the sin with no fear of ever missing heaven. That is exactly what i've been told by pastors who teach that doctrine. So even if it were the case that once you are saved you are always saved.. There is no way it could be accepted now because of how many church leaders have exploited it into (as the Bible says) "a license for immorality". There is no benefit in believing osas except the benefit of believing you can sin without eternal consequence. The pastors have beguiled the Word of any authenticity. They have made it a book of mere suggestions, because either way you still get to heaven. "If you love me you will do what I command". That sounds clear to me.