Anyone with a job that requires them to talk to people with unknown numbers calling. There is one bias right there. Probably people who don't get that many cold calls outside elections, which must fit some sort of demographic as well.
But the better pollsters don't just call. They use various online methods as well. 538 lists the following methods, and rates a pollster higher if they use more of them:
Live — Live telephone interviews, including cellphones.
Landline — Live telephone interviews, not including cellphones.
Live* — Live telephone interviews, but FiveThirtyEight cannot confirm whether cellphones are included.
IVR — Interactive voice response, otherwise known as automated polls or “robopolls.”
Online — Poll conducted by internet; generally, this means by web browser, but it’s inclusive of text message or application-based polling of mobile phones.
Mail — By U.S. mail or other “snail mail” service.
>Anyone with a job that requires them to talk to people with unknown numbers calling.
Exactly this. I'm forced to answer a lot of calls even when I think it's 80% likely that it's a spam call. I own a business and need to keep my employees fed with work. My likelihood of landing a contract with a person drops by about half if I don't pick up the phone right away.
But the better pollsters don't just call. They use various online methods as well. 538 lists the following methods, and rates a pollster higher if they use more of them: