“Then some of the itinerant Jewish exorcists took it upon themselves to call the name of the Lord Jesus over those who had evil spirits, saying, “We exorcise you by the Jesus whom Paul preaches.” Also there were seven sons of Sceva, a Jewish chief priest, who did so. And the evil spirit answered and said, “Jesus I know, and Paul I know; but who are you?” – Acts 19:13-15
I believe that this happens all the time in ministry. People start churches, music groups, or outreaches “in the name of the Lord” but their hearts are not in it “for the Lord”. They are in it for themselves. They are in it for the fame or fortune. These ministries do not produce fruit because they are powerless and are not a threat to the enemy. The enemy uses them to deceive others. Make sure you are serving in God’s ministry, not your own.