So from now on we regard no one from a human point of view [according to worldly standards and values]. Though we have known Christ from a human point of view, now we no longer know Him in this way. (2 Corinthians 5:16)
How many times have we felt misled by someone, or duped into accepting someone to be something which they were not. Some people are skilled at deception and can pretend to be something that they are not, in an effort to gain from others, through the means of deception. We often judge people by their outward appearance but God looks at the heart. (1 Samuel 16:7)
When John spoke to us about false prophets, he warned us to test the spirits to see whether they are from God or from the Devil. (1 John 4:1). He states that whoever confesses Jesus Christ is from God. James goes a bit further to remind us that even the demons believe in God and tremble in fear. (James 2:19) So even people who profess Jesus Christ and claim to be Christians can operate with wrong motives.
I always remind people, that Judas ate bread from the same dish with Jesus and that still did not stop him from betraying him. (Matthew 26:23)
I am not suggesting, that we spend our lives, being paranoid and mistrusting of everyone. We cannot lock ourself into a cage, or build a wall around ourselves to stay safe from others. On the contrary, what I am suggesting is that we sharpen our spiritual senses and grow in Christlike maturity, in order to be able to discern good from evil. (Hebrews 5:14)
Discernment is a spiritual gift according to (1 Corinthians 12:10). To another the working of miracles; to another prophecy; to another discerning of spirits; to another divers kinds of tongues; to another the interpretation of tongues:
As children of God, Paul encourages us to desire the gifts of the spirit. (1 Corinthians 12:31) So if we struggle with discernment, then we can pray for God to increase this gift to us, so that we maybe able to distinguish between the different types spirits operating in others. In that way we can make better decisions about who to trust.
If you need wisdom, ask our generous God, and he will give it to you. He will not rebuke you for asking. (James 1:5)