Ethnompsychiatrists visit these tribes and then they talk to the spirit, trying to reason and negociate with it. Ultimately the person is never exorcised but the spirit agrees to not hurt the person they possess and be content...
Ethnompsychiatrists are in their brain. You can’t intellectually deal with spirits. They can fool all logic. It must be done from the heart and in prayer.
Also, you can’t bargain with a liar and dark spirits are properly referred to as “People of the Lie.”