If you don't qualify you can try again and it'll give you a new survey. The other day I did this, and I actually RAN OUT of surveys and never qualified for any of them, even though I was answering question after question for the better part of an hour. Once in a blue moon I will qualify and complete a survey, but I can probably count those times on one hand.
The survey companies are usually looking for a very specific audience, so sometimes it can be really hard to qualify for random surveys like that. I think that's part of the reason why they keep upping the payout - they need more people to try so they can get more who actually fit what they're looking for.