Do not be fooled by the flattery of bitter men.
If a new person in your church is bitter about a previous church, the elders and pastors should be suspicious. Church leaders would be wise to contact the previous church and ask about the bitter man.
Most likely, he ran away because he was being held accountable for his sins. It is very foolish to listen to the flattery of the bitter man. He will likely turn against the new church in time.
This does not mean the new church should not minister to him or share the Gospel with him, but that church should not abandon wisdom and discernment in order to do that.