And how do they correct for that? What assumptions are made in that process?
My point is --> this problem is the most basic and fundamental problem that is the focus of every pollsters existence <--
Asking questions is extremely easy.
Getting a 'truly random sample' is extremely hard.
Trying to factor in those things is 100% of the work, that's what they do, it's their job.
Some are better, some are lazier, some have better data, some are individuals, some are teams so it varies hugely.
When the conditions are controlled they'll have a better idea than otherwise.
Their job is not 'asking questions' it's 'figuring out how to get random samples'.
The entire world works around the legitimacy of authority.
Yes - the quality varies, and pollsters don't have a high degree of institutional authority.
But some do.
If you want to learn about 'institutional legitimacy' - go visilt Pew.
Pew is an extremely well regarded institution. They are extremely good at polling. Go look at their methods.
They are a long running institution with serious professionals, big budgets, people who really know waht they are talkinga bout.
It's the difference between getting diagnosis from 'a neighbour' vs a 'doctor' but in this case there is no specific qualification.
Some 'respected pollsters' are basically insiders who have been doing it for a long time, with relationships and credibility - others, more institutional.
Check out Pew, they are probably he closest thing to institutional professional as possible.
Political polling is inherently hard - they will be the first to admit.