Basically, there are two types of Clairvoyants . . .
1. Those who are simply effective con artists, who trick people into giving them info. without being aware of it. Some who give public demonstrations who have been shown to have off-stage aids tielling them what to say, while reading the person' personal info card that they filled out prior to the show. The reader uses a speaker while the 'clairvoyant' wears a tiny receiver (often near or in the ear).
2.Those who --though they may also pull similar tricks a those just mentioned-- they also request & receive help from the spirit realm. Although many don't believe that Satan or his demons really exist . . . they do. And, they seem to enjoy perpetuating the lie that there is an 'afterlife'. . . that people don't completely die at death. They may either divulge information to a 'psychic', or, sometimes mimic dead people. . . . Some of these spirits don't hide their mean side, while others do . . . sometimes even impersonating loving dead realtives, friends, or others having something to do with that person's past.
How could they be convincing in doing such impersonations . . . ? The demons have been around since before mankind's existence, so it is reasonable to conclude that they could remember personal things about dead people & their past. They may also be able to glean information from a living person's subconscious memory of those people. Whichever way demons get such information is irrelevnt . . . they are ALL frauds! Christ described their leader --whose steps they follow closely-- thusly:
"[The] Devil . . . That one was a manslayer when he began . . . Truth is not in him. When he speaks the lie, he speaks according to his own disposition, because he is a liar and the father of the lie." (John 8:44).
So, *NO* clairvoyant is to be trusted!
Clairvoyants, their aids, or even demons . . . can all make use of information on the Internet, as well. For example . . . Just the other day I was wondering what my grandmother's middle name was, and in looking for her full name in her obituary online, I actually stumbled onto one of my great grantdfather's names . . . AS WELL AS the previously unkown to me fact that he committed suicide . . . AND . . . HOW he did it! . . . That is just the kind of information clairvoyants use to impress their clients with!
Now, if I can find that kind of information *without even trying*, just think how *easy* it is for those who are actually searching for such information on a regular basis!
To learn more about these issues, I recommend to you the following sources:
"Psychic Secrets", an article by jamy Iam Swiss
http://www.randi.org/site/index.php/swift-blog/2204-psychic-secrets.html
"Debunking Psychics", a video with Derren Brown:
https://www.youtube.com/watch?v=UQ4uBqdLaXI
"The Demons Falsely Claim the Dead Are Alive", an article
http://wol.jw.org/en/wol/d/r1/lp-e/1101991215
"Who Is Satan? Is He Real?", an article
http://www.jw.org/en/publications/magazines/g200702/who-is-satan-is-he-real/