Mark Shea believes in ghosts. So does Peter Kreeft. An occult author praised by Hans Urs von Balthasar believes in them. A lot of Catholic authors through the ages cite them as proof of purgatory.
But the Bible says “the dead know not anything” (Ecclesiastes 9:5-6, 10). For more on the Biblical truth of ghosts, see Amazing Facts (and then the chapter from The Great Controversy, “Can Our Dead Speak to Us?“