Nothing, not even demonic possesion, can happen to us unless God permits it or God wills it.
But if we keep placing ourselves in a position where we open ourselves to unclean spirits, perhaps sometimes God seeks to correct us by handing us over to their power.
The seances and ouiji boards attempt to contact spirits, but we know that there are good spirits and evil spirits. The good spirits do God's will, they do not do our bidding or follow our fallen will. Thus when we "command" or "instruct" spirits how to communicate with us, the only spirits who will appear to comply will be the evil ones. And these spirits are not the souls of the deceased, since we know that the souls of the deceased are in the hands of God. This only leaves the possibility that they are demonic. And the demons do the bidding of the one who Christ called "The father of lies." They will use the opportunity of a seance to lie and pretend to be benevolent or benign. The people participating can become obsessed with the oiji board or seance (as happens with so called "Spiritualist Churches") and ruin their relationships, careers, reputations etc. And yes, they can (and have) become possesed.
But again, we must remember that nothing can happen to us unless God wills it or permits it. So demonic possession, while a possibility as a result of these practices, is not inevitable. And if it happens, it is meant to correct us.
If you enter a dynamite factory with a box of matches, and light them one by one, not every match will definitely lead to an explosion, but one of them might- so why would you do so in the first place?