Ghosts do exist. The bigger question is what are they.
These demons can stick around for centuries until a Christian happens by and commands them to leave. That's the only way they will go. With human empowerment, they can move things, pound walls and make sounds.
As for the mischievous Shamans, I bind the demons on them to silence & impotence. They have a wild ride back to their bodies without any of their demon-augmented powers!
There seems to be human souls staying around familiar people or properties. I find they can't be cast out because they are as human as I. Instead, I point to heaven, where Jesus is on the throne, and tell them to come to Jesus. They take my directions and are gone.