I asked how they are supposed to know. Saying that their job depends on insight into customers isn't explaining how they know. The only explanation you provide

I asked how they are supposed to know. Saying that their job depends on insight into customers isn't explaining how they know. The only explanation you provide is: from taking to people at parties. I fail to see how that is supposed to provide insight into how many books purchased by the public at large are bought with no intention of being read. Let's consider the problem. Presumably the majority of people who buy books that they have no intention of ever reading would never admit to that fact. How do you then figure out the numbers of such purchases? (Remember that the comment I originally replied to gave specific figures). How does being an editor somehow give you any meaningful insight into those figures?