Being a Bon-Buddhist I do really believe in ghost. But I don’t believe that the ghost is scary thing that we see in Ghost film and story books. What I take conviction is ghost is just a soul of death people. When someone dies then most of people take rebirth in other realms.
If he she had done virtuous and good actions in his/her lifespan, he will take rebirth in higher realms- God, Demi-God and rich and happy family of human being. On other hand if he had done bad or non-virtuous actions then he will take rebirth in lower realms- hell, hungry ghost and animal which are full of suffering.
When somebody could not take both of those realms, then his/her soul would wander around his house and for his left behind wealth. When his friends and family don’t speak and care him then gradually he starts to hurt them and others. And in the end his family need do welcome some powerful priest and need to show the dead person a path to other realms.
So it is totally depend on our own deeds and actions in our present lifespan. There are some saying in our culture, ‘Live and let live’, ‘Don’t harm if you don’t help’, ‘Other is more important then self’.