Jesus and the apostles told us all to be fruit inspectors.
[Mat 7:15-20 NASB95] 15 "Beware of the false prophets, who come to you in sheep's clothing, but inwardly are ravenous wolves. 16 "You will know them by their fruits. Grapes are not gathered from thorn [bushes] nor figs from thistles, are they? 17 "So every good tree bears good fruit, but the bad tree bears bad fruit. 18 "A good tree cannot produce bad fruit, nor can a bad tree produce good fruit. 19 "Every tree that does not bear good fruit is cut down and thrown into the fire. 20 "So then, you will know them by their fruits.
[Jas 3:9-12 NASB95] 9 With it we bless [our] Lord and Father, and with it we curse men, who have been made in the likeness of God; 10 from the same mouth come [both] blessing and cursing. My brethren, these things ought not to be this way. 11 Does a fountain send out from the same opening [both] fresh and bitter [water?] 12 Can a fig tree, my brethren, produce olives, or a vine produce figs? Nor [can] salt water produce fresh.
[Gal 5:19-21 NASB95] 19 Now the deeds of the flesh are evident, which are: immorality, impurity, sensuality, 20 idolatry, sorcery, enmities, strife, jealousy, outbursts of anger, disputes, dissensions, factions, 21 envying, drunkenness, carousing, and things like these, of which I forewarn you, just as I have forewarned you, that those who practice such things will not inherit the kingdom of God.
[1Co 5:12-13 NASB95] 12 For what have I to do with judging outsiders? Do you not judge those who are within [the church?] 13 But those who are outside, God judges. REMOVE THE WICKED MAN FROM AMONG YOURSELVES.
[2Co 13:5 NASB95] 5 Test yourselves [to see] if you are in the faith; examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you--unless indeed you fail the test?
[1Jo 3:18-19 NASB95] 18 Little children, let us not love with word or with tongue, but in deed and truth. 19 We will know by this that we are of the truth, and will assure our heart before Him
[1Jo 3:24 NASB95] 24 The one who keeps His commandments abides in Him, and He in him. We know by this that He abides in us, by the Spirit whom He has given us.