So he sells these paranormal items to people who CAN'T see "them", to see if the spirits react to the items at all.
On top of that, every location he brings them to isn't actually haunted, but a nearby spot IS, probably to not put people in harms way (if a ghost mistakes a wandering eye as 'seeing it', it could probably have an effect on somebody who CAN'T see "them")
An actual psychic, posing as a fake psychic to sell "Junk", that actually turns out to be real tools used by real psychics in their testing phase.
That's some Kaiki Deishuu level trickery right there.