One thing that I would like to suggest (not sure if this has been discussed above), but not only have your team go in blind (so they don't know where they're going), but also do a mix of places where ghosts have been reported, and places where nothing has happened, as a control.
Of course, the danger is that if you take your group in an un-haunted location and they "claim" to experience activity, they could retort with, "hey! we've found a new haunted location!" So, you can't win.
As for claims of activity, I am always very dubious. I am contacting many venues asking if they have experienced anything fairly recently as even paranormal phenomena dries up. Some of them reply, "oh yes! We've had groups in and they experience a lot of stuff." Obviously, having been on a few of these ghost hunting bonanzas, the people there are so hyped up that even the tiniest thing is misconstrued as definitely due to ghosts; after all, why settle for a mundane, rational explanation when a supernatural one will suffice?! So, I ask if these venues have reports from people going about their day to day business? I find these are the most convincing, when people aren't thinking of spectres. Naturally, I put this very tactfully but a lot of venues don't reply. Its almost as if the don't want to feel conned or have their belief bubble popped.