It must be easy to fake so I'm sure there must be many who knowingly chance to fool folk, but since we do not know the nature of time it is an act of faith to say no one can get an impression of what is to happen. Although by the force of some folks arguments one would think proof was abundant.
You refer to fortune tellers, psychics, clairvoyants, which are not all the same. Fortune Telling is a general term and probably accurately describes those with no ability to see future events. Anyone can make up a "fortune" and tell you.
Psychics are folk who have (or claim) occult talents, and that can include clairvoyance, but could be other talents such as psychometry or clairaudience maybe. Clairvoyance is the name given to the ability to see future events.
I think your best bet is not to make assumptions but to treat such claims with suspicion until they have been demonstrated. Someone demonstrating such talents when they are personally gaining nothing material from doing so, is worth experiencing.