I’ve often wondered about the validity of polls in general, for a few reasons:
1 - the sample is biased right off the bat to people who are willing to answer the damned thing. I usually refuse to participate in any poll for anything, on the general grounds that somebody who wants to detain me for some inane poll can simply blow it out their ass. I suspect that you would find a significant difference in the honest opinions of the populations of people willing to participate, and the people who tell the pollster to get lost (who may, nevertheless, eventually vote, purchase the type of product the survey is concerned with, etc.). Unless you could compel people to participate in the poll, I don’t see how you get an unbiased sample.
2 - whenever I hear one of those polls with absolutely preposterous results like “90% of Americans think Fidel Castro wrote the Declaration of Independence”, I wonder how much of it stems from people messing with the pollster’s heads. Another reaction to being annoyed by a pollster can be to simply give idiotic answers to amuse yourself. I’ve been known to do that a couple times, too - “Yes, I believe the recent floods are God’s retribution for our sinfulness” (snerk, snerk).
3 - you might lie on the damned thing just to get through it in the quickest way possible, if you know that certain answers are going to elicit more detailed questions. I’ve been taking my car into the dealer regularly for its scheduled free maintenance, and I absolutely can not keep both the local dealer and the national organization from conducting two separate “customer satisfaction” surveys afterwards, and there doesn’t seem to be a tactful way to tell them “no, I don’t want to answer the survey, goodbye”. I’ve learned to just answer all “scale of 1 to 5” questions with “5” to avoid being asked a followup question about what I didn’t like about the service (“Finally, is there anything we can do to make our service better for you?” - “Yeah, don’t conduct these surveys.” usually nets a very defensive answer, too).
4 - I don’t care how anonymous a poll is, people are going to lie simply because they are ashamed to tell the truth, rather than reveal their dirtiest secrets. In political terms, you will have people saying that they are going to vote for the candidate reflecting their professed ideals, say the Green Party candidate, then get into the poll come election day and vote for the incumbent Republican congressman because he delivers great pork barrel.
Add these to the OP’s concerns about strategic lying on the part of the poll recipients, and one has to wonder.