I have lived in Seoul for almost 10 years now. This story line is pretty good and I can say that the cultural bits were spot on. The sets were atrocious and nothing they showed, except for the flashes when changing scenes, was even close to what Itaewon and Gangnam look like. Elementary schools don't even look like the cram school the two white teachers worked at. I honestly expect better from the set designers. Koreans don't even use dumpsters unless it is in the middle of a large apartment complex, let alone at a convenience store. They have designated spots to stack their trash bags on designated days. This is all info that could have easily been discovered.
It makes me wonder about the other episodes I have watched. How much research did they put into the locations? I hope it was more than 5 minutes of just sticking signs in different languages around.