-2 Corinthians 11:14 tells us that Satan can disguise himself as an angel of light. Demons serve Satan, and take after him. Why can't a demon disguise itself as a good angel, a dead person, a wise spiritual 'master,' or any other spirit that humans seek?
The spirits responding to contact are not dead people or wise spiritual beings, but evil spirits. The messages from these spirits may mention God, but they never urge Bible study, worship of God, or the need for Christ as Savior. The spirits deny Christ as the Savior or distort His message. God had some pretty harsh words for false prophets who were telling their dreams as though they came from God. This is not too different from claiming to receive messages from the dead and saying that God approves of this, or that it is a good thing, when God has clearly forbidden such contact. This is what God had to say about the prophets who presented their dreams as coming from God, when they weren't:
"I have heard what the prophets say who prophesy lies in my name. They say, 'I had a dream! I had a dream!' How long will this continue in the hearts of these lying prophets, who prophesy the delusions of their own minds? They think the dreams they tell one another will make my people forget my name, just as their fathers forgot my name through Baal worship. Let the prophet who has a dream tell his dream, but let the one who has my word speak it faithfully. For what has straw to do with grain?" declares the Lord. 'Is not my word like fire,' declares the Lord, 'and like a hammer which shatters a rock?'" Jeremiah 23:25-29
We cannot get information from God through spirit contact. We don't need guidance from wispy spirits playing charades. We don't need a medium, channeler, or psychic contacting spirits who are playing with our minds and preying on our grief. Instead, God gave us His only son, and He gave us His word in scripture. Through trusting in the work of Christ on the cross as the atonement for our sins, we are reconciled to God. Jesus, who has power over all the spiritual realms, has this to say:
"I am the First and the Last. I am the Living One; I was dead, and behold I am alive for ever and ever! And I hold the keys of death and Hades," Revelation 1:17b-18
For a more detailed discussion of this topic, see article by author published in the Christian Research Journal, "I See Dead People: A Look at After-Death Communication."
For more information on good and bad angels, see:
"Angels: The Good, The Bad,
and the Ugly," by Sue Bohlin.
Also, see the book, Angels Among Us, by Ron Rhodes.