Surprisingly badly paid. I wonder how strongly quality would track pay? Probably they act as a CAPTCHA mutually cross checking and so QA is by volume, and not coincidentally demands they work in isolation.
Quality control is often indeed by volume. When I was at Google / Facebook, search evaluations would typically have 5 raters each. One of the difficulties, though, is that search evaluation can be quite subjective. And honestly, most of the search engine raters we used were low quality and did a bad job (so the aggregate answer was often nonsense).
This. In the early days of my SQR rating time, the rating was not sliced into time per rating. And you had to write a short blurb about your reasons, often using the acronyms so it read like "NR, LQ / SPAM". Later you would see the other SQR notes and would wonder if both of you had seen the same page.