There's a long tradition of telling "true" horror stories, from accounts of serial killing to haunted house memoirs like The Amityville Horror.
The Conjuring is most definitely in this latter camp, and this trailer won't let you forget it. Cut in with footage from the film are interview clips with players in the real life events that the story is based upon.
Of course, this kind of marketing wants you to follow through and believe the ghosts are as actual as the people who claim to have encountered them. Well, no. I won't. There's no such thing as ghosts.
Still, it's ultimately irrelevant. This looks like a scary film and that's all I really care about. Can't wait to see it.