I don't know much about their methodology, except that they say they poll moviegoers at the theater. And that is a more appropriate approach than going by internet reviews, which will be a biased sample. Of course, you're still going to have considerations such as sample size, random selection of theaters (or not), and bias in terms of who does or doesn't respond.
Their website says the sample is "statistically robust," which is on the right track.
Their website says the sample is "statistically robust," which is on the right track.