What is the number of votes that gives a reliable indicator?
My answer is 25.
Here is an example. I asked the question - will you vote for Lee Hsien Yang if he stands in your constituency.
After 25 votes, I got the answer - 80% yes, 20% no.
When it reached 100 votes, the proportion is still the same - 80% yes, 20% no, with a margin of difference of maybe 2%.
I have observed this pattern for many of the Facebook polls that I have taken.
The statistician will state that a sample size of 25 is quite reliable for this kind of yes/no poll.
Many of the surveys in The Wisdom of the Crowd have more than 50 votes. I believe that the results are quite reliable.
There will be some bias if the questions tend to be political and a large proportion of the voters are pro or anti govt.
But for non political issues, the results are quite reliable.