Know them who labor among you. How? By their fruit. Not their works, degrees or spiritual pedigree.
Why not works? The gifts and calling are without repentance. One can perform works through their gifts and not have an intimate relationship with God.
Why not degrees? Degrees are not an indicator that one is walking closely with the Lord. In fact, when I earned my doctorate in 2008 I spent a lot less time in fellowship with God than I do now. Why? I simply didn't have the time. There weren't enough hours in the day.
Degrees don't give you the juice (anointing and grace to bear fruit) . When I was in seminary I saw adultery, fornication, uncleanness, lewdness, idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies, envy drunkenness (regularly smelled marijuana in one particular building), and revelries ON CAMPUS.
Meanwhile I know some folk who may not always get their subject-verb agreement right but know how to get heaven and earth to agree through prayer.
I'm not saying one cannot be educated and oily (anointed). I know some REALLY oily professionals- lawyers, doctors (of letters and medicine), publishers, public administrators, etc. What I'm saying is education or lack of should not be a yard stick for assessing the grace of God on a ministers life.
Why not by their spiritual pedigree? Just because their mentor or spiritual authority/father/mother has the juice doesn't mean they have it also. Many ministers are ordaining people to simply build a network. They're not pouring into or mentoring those they ordain. Or they're only pouring into a select few (sometimes those who make largest financial contributions). They're dead beat dads or moms. They have many so-called sons and daughters but aren't fulfilling motherly/fatherly duties.
Why by their fruit? Intimate fellowship with God gives us grace- divine enablement, to bear fruit. Fruit of love, joy, peace, gentleness, goodness, kindness, faithfulness, patience, and self control are born out of intimacy with the Holy Spirit. Those who bear this fruit re-present God in the earth realm and are recognized in the realm of the spirit as God's ambassadors. These are the sent ones who show up in the character and nature of God.