I could mock up Certificates of Haunting with previous little girl owners telling their horrible stories. Sort of a short story version of the Mounted by a Monster series of books.
I personally wouldn't be deceitful on EBay and tell people a doll is haunted when it's not. I'm sure a lot of people do that though.
I go to a horror movie convention every year and there's even a few vendor booths set up with creepy dolls that people bought and painted up. They have barbies, cabbage patch dolls, thrift store dolls, etc. Some people even turn Elmo into a scary doll. People love that stuff.