The false prophets are ashamed, not in the sense that they are convicted and ashamed before God at what they have done, but in that they must do it secretly, knowing it to be wrong. In New Testament times, in the true church, there will be no prophets like these wandering visionaries described by Zechariah; there will be clarity and true teaching.
You can tell a false prophet by the scars of his record. The picture is of error having to act sneakily and come in by deception, because open error will not be tolerated in the church of Jesus Christ. The pastors and elders in the church of God must have their eyes open, because error, when it comes, will not parade itself openly. Paul warns the elders in the passage quoted above that it will not be easy to spot error, but that it is sure to try to make its entrance. Where the ministry is effective and the truth is clearly taught, error will be forced to keep its head down.