if there is no plausible sampling frame available for surveying, how will one obtain a representative sample of size n.
In the textbooks they use SRS, stratified, cluster, and systematic but these all imply a sampling frame is available like a telephone book etc.
So say for example, there is a website selling old cars, but they don't allow you to list them all, but you can search by make or model. How would you in this case get a representative sample of size n?
Or if we were trying to get a representative sample of size n to survey the number of library books that are borrowed but we don't have access to the entire catalogue?
But representative sample in the sense we can use it to make inferences about the population.