Fruit inspector.
Matthew 7:16 You will know them by their fruits. Do men gather grapes from thornbushes or figs from thistles?
17 Even so, every good tree bears good fruit, but a bad tree bears bad fruit.
18 A good tree cannot bear bad fruit, nor can a bad tree bear good fruit.
19 Every tree that does not bear good fruit is cut down and thrown into the fire.
20 Therefore by their fruits you will know them.
Jesus makes these difficult spiritual issues so very easy to understand. Look, a good tree cant make bad fruit. Look, a bad tree cant make good fruit. People are the trees spoken of. Fruit are their actions or works. Is the false prophet producing bad fruit? There is your easy answer. Its not about having an off day, if the works are bad, its because they have a bad heart. All starts in the heart. Just let people talk, you will know quickly of whom they belong. You dont need a private eye to trail them, just examine their fruit, as Jesus just said.