When you visit a psychic performance they have usually either hired actors to sit in the audience and be amazed, or they carry out some research on the people in attendance which is shit easy in this day of peoples lives playing out on the internet. You book tickets and you have already given them enough info to search out your details.
If you log on to them online, youtube or otherwise then you do the same, it is easy for them to dig up some details they can use.
For general predictions, its just picking out the most common of things that can apply to many and hoping that someone will see a match to their own lives, and if they really want to they will.
Can you give us an example of what they said and how you believe it was specific to you?
Its a load of bollox, these tricks havent changed much over the last hundred years, the only difference now is that it is super easy to find details on people these days, making the 'psychics' job a little easier.