What an Image Cannot Tell You
But the LORD said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the LORD seeth not as man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart.
1 Samuel 16:7 KJV
A confident manner can make a person seem trustworthy before you know anything about his character. Samuel was impressed by Eliab's appearance, and the Lord corrected him. First impressions are not complete knowledge.
God looks on the heart. You and I cannot do that perfectly. We should not use the verse to claim that we know someone's hidden motives. It should make us more careful, not more certain about guesses.
Look for honesty, humility, and consistent conduct over time. Avoid ranking people by appearance, influence, or the quality of a profile. Examine your own desire to seem impressive too. The Lord already knows what is behind the image. Give more attention to becoming trustworthy than to arranging the quickest appearance of it.
Keep the passage in context
God corrects Samuel's judgment of Eliab while choosing Israel's next king. Outward appearance does not give a complete measure of a person. The LORD knows the heart in a way human observers cannot.
Read further: 1 Samuel 16 in the King James Bible.