Seems to me there are studies which could be done where you'd really have to stretch the definition of participants to say that non-believers are interfering. For instance, if the test is say telekinesis, skeptics don't have to be physically present and could swap in believers. Mechanical devices could be created for psychic card readers (clairvoyants and not telepaths obviously). I see no reason why prediction require the skeptic to be present, same with remote viewing.
The world is so vast and we have so much recording equipment that it seems telling that we only get after the event accounts. I've yet to see some psychic out of the blue really come up with something. What I do see, are interviews with psychics bragging about how helpful they were.
I think it was Penn of Penn & Teller who pointed out that if the psychics didn't see 9/11 coming then they're BS.