The details. When a person shares a ghost story and includes specific details like the time, place, and what they actually saw or felt, it makes it more believable. For example, if someone says they were in a specific room at 3 am and saw a white figure with long hair floating above the bed, those details create a vivid picture in your mind.
The fact that they often involve ordinary people in ordinary places. It's not like these are stories from some far - fetched, made - up world. A person could be in their own home, a familiar place, and then something strange happens. They might see a door open by itself or feel a cold hand when no one else is around. These are the kinds of things that could happen to anyone, and that's what makes true ghost stories so believable.
Often, it's the emotional aspect. If the person telling the story is visibly shaken or still seems scared while sharing it, you're more likely to believe it. Also, when multiple people have similar experiences in the same location. For instance, if several people claim to have heard strange noises in an old mansion, it gives more credence to the story. There's also the element of the unexplained. If there's no logical explanation for what they witnessed, it makes the ghost story seem more real.