How biased is the survey likely to be? Now, it is hard to take a few hundred sample size and be unbiased by any measure. Given that, I wonder what specific kind

How biased is the survey likely to be? Now, it is hard to take a few hundred sample size and be unbiased by any measure. Given that, I wonder what specific kind of bias does posting a survey on mturk throws up, since the survey takers are actually "working".