You can't take an "unbiased" sample in the sense that you mean here.
There's only one way you can take a completely unbiased sample: if you know exactly how everyone will vote in advance and select them carefully on that basis. But if you already know how everyone will vote in advance, then sampling is a fruitless exercise.
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The result of your sample would typically be anything between 30% and 100%.
Whereas, if you instead take a sample of 1000, you typically get results between 61% and 69%.
Source: http://www.wolframalpha.com/input/?i=binomial%2810%2C0.65%29...
You can't take an "unbiased" sample in the sense that you mean here.
There's only one way you can take a completely unbiased sample: if you know exactly how everyone will vote in advance and select them carefully on that basis. But if you already know how everyone will vote in advance, then sampling is a fruitless exercise.