It isn't just a Halloween thing anymore:

Ghost tourism has boomed over the past decade, propelled by the public's interest in the mysterious and supernatural. There are hundreds of ghost tours offered across the country, from Hollywood ("Come see Haunted Hollywood and ghosts of the stars!") to New England ("Visit Boston's infamous haunted locales!").

Some places have more historical lore to draw upon than others. Salem, Massachusetts, for example, exploits its infamous witch trials of the 1690s, while tourists, goths, wannabe vampires, and Anne Rice fans flock to New Orleans, Louisiana, with its reputation for mysticism and voodoo.
[...]
Ghost tours can be a very lucrative business: It is a service with little overhead and start-up costs. Anyone can offer a ghost tour, and tickets often cost $10 to $30 or more per person. With a large group, a good storyteller can make $500 in one evening for guiding a walking tour and telling ghost stories. Everyone likes a good ghost story, and the tours can be fun. The best ones tell their audiences about fascinating local history, throwing in some spooky lore as well.