It is easy to bias a sample of 10,000 people. On the other hand, a sample of as few as 200 people can accurately represent the feelings of an entire nation if the research is conducted properly. Only if the sample of people interviewed is truly representative of the overall population is the study reliable. Surveys conducted during conventions, for instance, are only representative of the people attending the convention. If you know the sample was reliable, and you know how the questions were phrased, you're most of the way toward determining if the research is valid.
Biased questions provide biased data.
Yet surveys much more biased than this have received media coverage. Far more insidious is the study that is biased not by what it asks, but by what it doesn't ask. For instance, it's not uncommon for liberals to promote a survey which shows Americans want more government spending, while conservatives have a competing survey proving Americans want lower taxes. Paradoxically, Americans often desire both higher government spending and lower taxes. They want the best of both worlds.