A couple of years ago we were attending a party and a man there read a few palms. He didn't know anybody else at the party but apparantly he was 100% accurate with what he was saying. When he got to mine, he said there is so much going on that he couldn't do it then but I should see him privately. Now he did not do this for a living, he never accepts money, he just said the "gift" ran through his family. This worried me a bit but I just never got around to seeing him again. For the next year life was like a roller coaster, so much went on.. I'm hoping that he'll be able to tell me that everything the other guy foresaw is coming to an end!
It's generally the law of percentages - I've read quite a lot about how people can believe in stuff like this, and in illness terms it usually boils down to pointing to the head or stomach, as 90% of ailments have at least some symptoms in those areas.
You will often hear quite general terms, that people who desperately want to believe can twist to a great degree to make it fit what they want to hear. Safe to say, no-one has ever even come close to replicating convincing results under test conditions.
I'm not necessarily saying the bloke is a con-man by the way - one thing James Randi (the chap offering the 1 million dollar reward I posted earlier) makes a point of saying is that often these people genuinely believe they have a gift, and the feedback they get from clients provides a positive feedback loop that keeps them going, and strengthens this belief in their own "abilities"
You just have to look at someone like Derren Brown to see how some people can be astonishingly good at discerning information from the slightest of clues, but this is a strictly human ability - there really isn't anything supernatural at play in my opinion.