CactusJack, the best idea would be to point out that there is zero science involved in ghosthunting.
Depending upon what equipment he brings, I can advise a tad.
If he has a Trifield Meter (EMF Detector) point out that there is no reason on the planet why a spirit should manifest itself as an electromagnetic field. Also point out that those meters are calibrated to measure the fields of household appliances, so unless he has the spirit of a Mr. Coffee, it isn't going to read.
Also recommend that he turn the Trifield Meter on and point it at his forehead. Be sure to ask why exactly the needle doesn't move. And, since it doesn't move when it's pointed at an actual human being that still has the "spirit" inside it, why would it when the spirit is removed from the body?
Add also that the only thing electromagnetic fields have to do with science so far is the Persinger experiment which is working to prove that some types of electromagnetic fields cause hallucinations (including feelings of being watched).
Then, if he brings out an Infrared Thermometer, you can also say that those do not measure air temperature (ghosthunters use them to measure cold spots). Suggest that he point it at you. When it reads your surface temperature at around ninety degrees, offer to step aside and have him measure the same piece of air he was supposedly measuring before. If he points the thermometer at the same spot, he will actually read the wall behind where you were standing. The temperatures will be different. Tell him this should be impossible if he was measuring the air temperature.
If he brings in dowsing rods, suggest that you cover two opaque glasses, one of which contains water and one does not. Have him dowse for the one with water at least twenty times. If he is not right every single time, then dowsing rods are not scientific instruments and do not work.
If he brings in EVPs (Electronic Voice Phenomenon) ask him to play a clip without telling the audience what it is supposed to say. Ask him to allow the audience time to write down what they believe it is saying without discussing it. If they get multiple answers, then the ghostly voice is not saying something definite. If it's not saying something definite then there is no way to get meaning from it.
If he shows an orb photo, talk about dust particles, shutter times, the effect of flash...
Above all, point out that since there is no proof that ghosts exist at all, gathering evidence of them makes no sense. The first step is to prove their existence. Only after that can any tests be done on what they can do.
Here is some stuff from when SAPS talked to the DFW Ghost Hunters group...
http://skepticalanalysis.com/id90.html