Once you've found an investigator you're comfortable with, ask him how long he's been involved in paranormal research, and about his past investigations—especially those involving private residences. If he claims to be some sort of "doctor," ask what kind of doctor he is. Find out if he's affiliated with a research group or a national organization, such as the American Ghost Society. Being affiliated with a group with a good reputation can help you make a better decision about allowing him into your home. You can also call the organization and request additional information.