Very interesting subject, and I have a story: When I purchased my condo and moved in, I unpacked everything bewfore deciding where to put things. One item in particular was an English Clock with a glass dome, with 4 globes at the botom that moved, operated by battery, but no battery was in the clock. One day I came into the bedroom where the clock was and it was operating, with the correct time, but no battery was in it. The next day it wasn't operating, but it was several days later. This went on for a few weeks, along with other small things being moved. I happened to mention this to my neighbor who had been in the building several months longer than me, jokingly saying I had a "guest". My neighbor then told me the story of a homeless person dying in a fire when the building was left unattented during convertion from apartments to condos. And, he says, the death occurred in what eventually became my condo (the bldg was gutted and those units were enlarged to create the condos). I never had a problem with my "guest", and never rearranged anything that was changed, presumable by him. I guess he was content, and I never thought anymore agbout it.
Then one calm spring day I was reading in the living room when I felt a cool blush of air against my cheek, heard a tinkle (like a high-pitched bell), and saw 2 slats of the verticle blinds at the balcony door shimmer (the door was closed and locked). At that moment I experienced a very strange calming sensation, and remember saying aloud "goodbye". When I next went into the bedroom, the clock had stoped at the exact time my "guest" departed, and it has never worked since..about 5 years, and still shows that time.
I like to think my "guest" is now at peace in a place of his choosing, but if ever he decides to return, I think it will be acceptable as he was not the destructive ghost/spirit we hear about, but a kind one, and he had a sense of humor (based on some of the "happenings" he engaged in).