It's not just who they call (for example, if I want a certain response, I can either call Massachusetts or South Carolina), but the questions they ask as well.
I think we had a good example of this here on these boards. Somebody asked, "Is Bush the worst president ever" and the choices were:
1) Yes
2) He's the best president ever
3) It doesn't matter to me (or something like that)
4) I don't know.
So your choices are to either say that you think he is the worst president ever, or you think he is better than any other president in the history of the US, or that you couldn't care less about your country, or that you are just plain ignorant. Come, on where's the fairness in that kind of poll. What about, No, I don't think he's the worse president ever.
Most of these so called political polls are worded to get an overwhelming response in one direction. Another examle of today's polls.
Are you for our soldiers dying in Iraq?
No, I'm against the War
Yes, the War is a good thing.
Guess what, 85% of the people polled don't want our soldiers dying in Iraq. Of course not (who in their right mind does), but of that 85%, if you were to ask them, do you think it is important to do whatever it takes (including going to war) to prevent another 9/11, most of those same 85% would say yes.