That is why groups will carefully word questions to obtain responses that reflect their viewpoints. It does happen sometimes. I don't believe in polls. I've been all over the United States and have never met anyone who was ever polled. The first question I answered earlier.
Polls are often quite accurate as snapshots.
Overall, they're a useful indicator. To some extent and for a short period, yes. People are influenced by all sorts of considerations and poll results are often extraordinarily sensitive to a myriad of factors. One way in which they may be influenced occurs when their candidate is way ahead in the polls. They may stay home.