I'm not going to get into the over-arching point on a board inhabited by subscribers to scientism, but don't you think the jig is is kind of up if you're told someone has a scar through their right eye and they actually didn't, or that someone had a favorite shirt that has a tear in a certain place (that both of those things didn't exist, etc).
In other words, a level of specificity that is not so easily dismissed as a scammer interpreting the information they've been given.
Anyone with supernatural powers that takes that offer is a fool - their life would be effectively over. A person that could, say, see the future, is better off predicting the winning lottery numbers and sidestepping the almost certain involvement with government agents, or worse.
(Not that winning the lottery is statistically a good thing for one's quality of life either, which is a plausible reason that "psychic wins lottery" has never been a headline...)
This is about the future, but I think can be applied equally derisively to talking to the dead. Also My Dinner With Andre is a great movie so why not share it here:
In other words, a level of specificity that is not so easily dismissed as a scammer interpreting the information they've been given.