Not really because really only God knows what is in someones heart.
But we can judge them based on what we think is a correct assertion by noting and investigating. But we are forbidden to spy just look at what is obvious.
4:94 O you who believe, if you go forth in the cause of God, you shall investigate carefully. And do not say to those who greet you with peace: �You are not a believer!� You are seeking the vanity of this world; but with God are many riches. That is how you were before, but God graced you, so investigate carefully. God is expert over what you do.