I know someone who is a psychic medium as a profession, working on one of these psychic hot lines. As far as I can see she acts as an agony aunt to some very troubled people, giving common sense advice about life. She has never to me shown any pyschic abilities but people return to her for advice time after time.
I have visited a "fortune teller" at a fair, she utterly amazed me with the stuff she told me, I was in there a relatively short time she didn't know me from Adam but boy was she accurate with what she told me. In fact I have been approached a couple of times by people who have a message for me, no money exchanged hands, the advice was unsolicited but was always given when I was going through some personal turmoil. In each case the message was helpful.
Personally, I get very strong feelings about certain things. I have this thing going on where someone I know will pop into my head, then they invade my dreams and my thoughts, I have found that I get a desperate "need" to get hold of this person. Invariably this person has something going on in their lives and they just need to talk it out with a non involved person! I have never been wrong.
In summary, I think those people who charge for their "gifts" are just very good at reading people and situations, however there are people out there who do just know stuff but would never dream of profiting from their gift and only say something if they think they can help.