My ex is friends with one of the guys that WAS on that show. I don't believe he's still on it, it was one of the earlier seasons when they had their "live" episode. Any way, it goes like this:
1) The show is real
2) Some of the tools used are theory, not proven, are a gimmick
3) Everything they catch on camera is authentic
4) They have been tricked before by the residence of the estate itself, looking for publicity
Now, what it boils down to: Do you believe when something super-natural occurs in the show, that it is indeed para-normal, or rather an anomaly that could be explained in the realm of science of solid material were present, etc.
As for me, I don't like believing in wandering spirits. Stems back to my private school days, but I will concede to the possibilities.