You may not know what is in their “heart” (minds NASB) (3820) but you can hear their “lips” (8193). Jesus put it another way,
(Matthew 7:20 KJV) Wherefore by their fruits ye shall know them.Fruit is not immediate. Sometimes fruit never comes. We had a fruitless mulberry tree in our yard. In looking it up I found a long list of fruitless trees including plum, olive and fig. A fruitless tree is only there to look cute. It does not produce anything of value. It is a promise without a fulfillment.
The quality of fruit is not in how it appears. I have seen some apples that looked beautiful but when you bite into them they are pithy and tasteless. It is only when the apple passes the lips that you know its worth.
So? Listen to people. What is the result of their talk. Ask yourself if they are the kind of influence you need in your life.