To mislead people, the demons use spiritism. The practice of spiritism is involvement with the demon's both in a direct way and through a human medium. The Bible condemns spiritism and warns us to keep free from everything connected with it. Galatians 5:19-21 "But when you follow your own wrong inclinations your lives will produce these evil results; impure thoughts , eagerness for lustful pleasure, idolatry, spiritism, that is, encouraging the activity of demons), hatred and fighting, jealousy and anger, constant effort to get the best for yourself, complaints and criticisms, the feeling that everyone else is wrong except those in your own little group---and there will be wrong doctrine, envy , murder, drunkenness, wild parties, and all that sort of thing. Let me tell you again as I have before, that anyone living that sort of life will not inherit the kingdom of God." (Living Bible) Spiritism does for the demons what bait does for fishermen. A fishermen uses a variety of baits to catch various kinds of fish. Similarly, wicked spirits use different forms is spiritism to bring all sorts of people under their influence.
For Poltergeist to come they need to have a purpose behind their unfinished business. Someone would experience a poltergeist if there are unusual things occuring in their house. Also they come to those who can contact them e.g. Mediums.