>who checks the sources
I do, when I’m reading something and accuracy matters. Anybody who cares about accuracy will investigate the sources. I know people will complain that “nobody” does this, but it is essential, without checking sources you are just casually reading. That goes for books and all media consumption. If a book or any media (ahem Tucker) doesn’t give you enough information to be able to look something up, that is rather a red flag of obfuscation.
The thing is, there’s really no good way to check a lot of the numbers you see in sources like the World Factbook.
Take population estimates for instance. Much of the world either doesn’t have the state capacity or can’t be trusted to maintain accurate, publicly known population figures. There are some countries where they haven’t had a census in decades and their official population figures are entrusted to numbers provided by regional governments which receive national funding on a per capita basis. Every region has an incentive to inflate their population numbers and, in a system where they’re all competing for funding from the central government, this eventually becomes common practice. Even national governments have little incentive to share honest figures with the rest of the world, and national governments that aren’t even accountable to their own people like China and Russia are also well practiced in keeping secrets. And population is probably one of the easiest things to measure.
The problem is that some people just accept the first number they find and are militant about not thinking beyond that point. If you tell them the radiation meter tops out at 3.6 roentgen, they say “3.6 roentgen, not great, not terrible”.