Proverbs 14:5 A faithful witness will not lie: but a false witness will utter lies.
6 A scorner seeketh wisdom, and findeth it not: but knowledge is easy unto him that understandeth.
7 Go from the presence of a foolish man, when thou perceivest not in him the lips of knowledge.
In these verses a faithful and righteous person will always tell the truth and be humble enough to seek knowledge and be taught and last to stay away from those who will lead you in the wrong direction.
We also have those who every other statement they make is a lie and has no idea where to look for knowledge and the language they use is not what you want to be around
Sometimes we have to make hard decisions on who we need to witness to and who not to. But if we will continue to seek the wisdom and knowledge of God and pray for discernment He will help us to identify which is which.