Identify the sample. The survey should state the population from which it was sampled. This is the group of people who had the possibility of being chosen for the survey. A survey may state this explicitly (e.g. "The sample was taken from a database of past employees") or implicitly (e.g. "This study asked students at the University of Washington the following questions"). If the sample does not match the population of the study (for example, the sample was a group of American-born Chinese people, but the results are making inferences about Chinese people in general), then the results of the survey are invalid.
Locate the sample size. This is the number of people who were included in the survey. Again, the sample size can be clear (e.g. "48 people responded to our survey") or obscured (n = 29). The letter "n" typically refers to the sample size in survey studies. If the sample size is less than 20, it is most probably too small and the survey's results are probably invalid.
Find the sampling method. The sampling method is the way in which the sample was collected. Common means of sampling are randomization, convenience sampling and snowball sampling. If the means of sampling is not clearly shown on the survey, then the survey is likely invalid. In addition, any sampling means other than randomization leads to biased results, and therefore a survey that employs a method such as snowball sampling is possibly unacceptable.
Detect any poorly worded questions. Survey questions must be simple and unambiguous to be considered psychometrically valid. In addition, multiple choice questions are most valid, as free-answer responses can often be interpreted in many ways. If you find too many long-winded or seemingly irrelevant questions, it is a sign that the survey may have been designed in an intentionally biased manner.
Observe the margin of error. If there are results stating that a statistical difference is present, look at the differences in the results and make sure that they differ by at least the margin of error. Otherwise, the survey cannot claim true differences were found.