Knowing where people are coming from is important. Listen to what they say but more importantly watch how they live.
Read: Titus 1:15-16
15 Everything is pure to those whose hearts are pure. But nothing is pure to those who are corrupt and unbelieving, because their minds and consciences are corrupted. 16 Such people claim they know God, but they deny him by the way they live. They are detestable and disobedient, worthless for doing anything good.