If Christianity was true, how do you explain ghostly appearance of people who had died?

This was one of the biggest arguments of the rest of the religions who believe ghost existed against Christians Believers. Nice argument I would say but if Christians are not able to understand the Scriptures of the Bible well, then they would not be able to answer the question. As usual, let list some facts:

1. How many ghosts (mainly those who died) that had been claimed to appear before other people are actually Christians? Meaning, were there people who died who were known to be Christians and had appeared as ghosts attempting to harm witnesses?
2. Even if they had seen spirits from Christians who had been called home, is never for bad nor harmful reasons. The appearances are always a sign of blessing, last wishes or forgiveness. But there seems to be a flaw in this: (LUKE 16:19-31) Jesus described indirectly that dead is forbidden to make contact and teach the living about after-life.
3. Now lets look at Devil’s 3 main purpose(Refer to JOHN 10:10):
1. Steal
2. Kill
3. Destroy
4. If you read Bible carefully, you will know how much God honors those who stay true to his words. You will then also believe that God will not allow the Devil or Evil Spirits to tarnish the name of his followers. To be more direct, the Devil will wouldn’t be able to use the images of faithful followers of God to scare or harm people.
5. So what is left for the Devil to play about if he wants to steal believers since Christians ruled out ghost existence, the devil will use all sort of ways within his means to deceive and draw people away from God via making ghost appearances.
6. But there is a flaw in this plan of the devil even if they had attempted to create images of dead Christians to appear to witnesses. As the Devil will not be allowed to meddle with the reputation of the God’s faithful followers, ghostly images appearance of Christians are created by the devils themselves, to sway the weak faith Christians BUT were unable to physically harm those witnesses who saw them.
7. However those ghostly images of people who had died and appeared to scare and harm are clearly the non followers of God.
8. The only one who can summon the real spirits is of course God himself as he is the ruler of everything including heaven and hell. MARK 9:2-9 describes Elijah and Moses talking to Christ in God’s presence.
9. So unless God permits it, you’ll never see Ghostly imagines of faithful Christians doing harm.

If you would like to read more about Christian view of Ghost, I do have some links for you. Take note that the Bible is still the best book for reference.

http://www.spotlightministries.org.uk/hauntings.htm