I don't believe in possession, but IF there are evil spirits that can possess people, then there would be good spirits with equal ability. So-called possession is a matter for a psychologist or psychiatrist.
I think there are no good spirits, just bad spirits, that being 1/3 of the angels throw out of heaven (demons). God gave us angels to watch over us...Psalm 91.11, For He will send His angels to protect you wherever you go.
Neither. The only "spirits" that exist are alcoholic, and likewise possession does not exist. These "possessed" people are suffering from mental health issues or mass hysteria, and are harmed not helped by people "casting out demons" or performing "exorcisms" rather than actually getting them the help they need.