Each method have it's own advantages and inconveniences. The behavior of populations and groups. You might end up with unexpected reactions. You can hardly imagine a survey without some kind of list. A list will give you the identification of who you should be able to reach.
Some lists are less than perfect.
A proper sampling is one of the master keys to build a good survey . If your sampling is inadequate regarding the goals of the survey, you're confronted with a major flaw. A list of links with more than 110 resources included. First, I studied Sociology at university and after, I've got my master degree in Ethics. My experience is mainly in the field of teaching sociology.