I'm not sure how I do that but I will take your word for it. I realize I'm in no position to judge who is saved and who is not saved. I understand that is for God to do. I merely try to point out error in understanding scripture.
Consider the PRINCIPLE clearly made obvious in a passage like the following...
1 John 5:13 These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.
It is obvious from passages in Scripture, like that one, that one CAN know from Scripture itself, whether one is saved or not.
Meaning only they and God can know that.
For salvation is a one on One personal matter.
All we can do is take their word that they actually hold to that which they are asserting, that is actually sound to begin with.
But the PRINCIPLE is CLEARLY taught in Scripture...
1 Thessalonians 2:13 For this cause also thank we God without ceasing, because, when ye received the word of God which ye heard of us, ye received it not as the word of men, but as it is in truth, the word of God, which effectually worketh also in you that believe.
Romans 5:6-8 being THREE MORE examples of the FACT that one CAN KNOW - not hope, not wonder - but KNOW that one IS...saved.