"Unreliable witnesses: The challenge of separating truth from fiction when it comes to North Korea" by Jiyoung Song, a former UN Consultant for the Office of the High Commissioner for Human Rights. The author writes:

I have interviewed North Koreans as a North Korea watcher and human rights researcher since 1999. What I’ve found suggests there are issues with the current methodologies used in investigating North Korean human rights and serious ethical dilemmas many researchers have to deal with. [...] North Korean refugees are well aware of what the interviewer wants to hear. Whether it is the UN COI, the US Congress or the Western media, the question has been consistent: why did you leave North Korea and how terrible is it? The more terrible their stories are, the more attention they receive. The more international invitations they receive, the more cash comes in. It is how the capitalist system works: competition for more tragic and shocking stories.

In my 16 years of studying North Korean refugees, I have experienced numerous inconsistent stories, intentional omission and lies. I have also witnessed some involved in fraud and other illicit activities. In one case the breach of trust was so significant that I could not continue research. It affected my professional capacity to analyse and deliver credible stories in an ethical manner but also had a deep impact on personal trust I invested in the human subjects I sincerely cared about.

And here is an article from Hankyoreh, south Korea's top center-left liberal newspaper: "The insidious threat of fake news surrounding North Korea", which says:

Time and time again, conservative outlets and foreign media circulate and reproduce rumors based on questionable sources [...] South Korean and overseas media have routinely collaborated to produce reports claiming that people had been “slain” or “purged” when they were actually perfectly fine. There tends to be a flow to the production, transmission, and propagation of this sort of fake news. The first report generally cites an “internal North Korean source” whose identity cannot be confirmed. Often, this is spearheaded by domestic news outlets like the Chosun Ilbo -- but once the government or foreign news outlets like CNN become involved, the reports tend to take off like wildfire. The result is an endless feedback loop, where the claims of a “North Korean source (or defector)” are published in the domestic press and then the foreign press, then republished in the domestic press and echoed by the administration, politicians, and defectors in South Korea. Notably, retractions and apologies are rarely ever provided when the reports are shown to be false.

And the case of Kim Ryun-hee: "A N. Korean mother’s quest to return home to Pyongyang", a woman from DPRK being kept in south Korea against her will (she is not the only person in this situation):

"... I’d been having problems with my liver, and I underwent treatment in Pyongyang. But when it didn’t get better, I decided to go visit relatives in China for two months to recuperate in May 2011. The hospital costs in China were so much more expensive than in North Korea. I worked at a restaurant in China to earn money to go back to North Korea, and that’s when I met the defection broker. They told me, ‘You can earn big money working in South Korea for just a short time.’ So I handed over my North Korean passport, and by the time I thought better of it, it was already too late." [...] In September 2011, Kim arrived in South Korea against her wishes, having been taken in by a defection broker. From her very first National Intelligence Service questioning upon her arrival, she has consistently demanded to be sent back, but her requests have been refused.

There are many cases of north Koreans stuck in south Korea against their wishes, Kim Ryun-hee is just one well-known case. Generally they are under surveillance by south Korea's intelligence services and get in trouble for publicly supporting DPRK, and some of them get framed, blackmailed, or tortured into producing false confessions of spying. A south Korean documentary called Spy Nation goes into detail about that. (Here it is on YouTube).