Its real easy to tell a real christian from the fake.
There is a big difference between saying you believe and really believing.
If you really believe then you will obey Gods law, If you ask for forgivness and you believe in Gods judgement you will not commit that sin or sin again, because that would be the same as commiting suicide.
A real christian would understand all these things and try hard to uphold the teachings of Jesus Christ. That is what being a christian is.