North Korea has had thousands of foreign workers, mostly aid workers, in its borders, and businessmen from neutral countries that have not signed up to sanctions are given privileged access to the country. They are more reliable sources on how the country operates than any "unnamed source".

The big name I can think of is Felix Abt, who wrote about life in Pyongyang. Bad, but much safer than most of the other comparable capitals he did business in. He's biased in favour of ending sanctions and sanitizes some of what he said, but "A Capitalist in North Korea" confirms some of the negative assumptions about the country while criticising the more extreme claims.