On my first trip to North Korea, our guide told us that the average summer temperature in North Korea had risen by 10 degrees in recent years, a fact he blamed on global warming caused by US pollution.
As a guest in the DPRK you've got two ways to react to information like this. You can cast doubt on the guide's information, or you can assume it to be propaganda and take it with a pinch of salt. If you do the former, you're making it more likely that that guide will be reluctant to open up to other questions, so a kind of unsaid agreement is reached: you don't ask too many questions you know the guides will find difficult to answer, and it turn you'll be allowed a little more leeway to take photographs and so on.
The guides are smart people. They're well-educated, they often speak multiple languages, and they're exposed to the outside world in a way that 99% of North Koreans never are. Many of them have travelled to the Middle East or Africa to study. They deal with foreigners every day who hold very different views to their own.
But they're brought up to believe that North Korea is paradise. They know that living standards are higher in South Korea, but they see it as American money, and they're brought up to loathe the Americans, so that wealth is tainted. And this view is reinforced every day, every where they go. The guides understand this is propaganda, and they know that what they're sharing with tourists is part of that, but as Pyongyang residents and people trusted enough to deal with foreigners, they're part of the elite, and they're willing participants.
It can get strange. A lot of the more nonsensical stories about the Kims actually emerge in Chinese tabloids, but if you ask a guide whether Kim Jong-il really did play a round of golf that included 18 holes-in-one, you won't get a denial because they don't want to cast doubt on his sporting abilities. Once I saw an air stewardess on an Air Koryo flight burst into tears because a tourist accidentally stood on a newspaper bearing a picture of the Dear Leader. Was she upset, or playing the part expected of her? It's really difficult to tell.