It might be a very professional school, but you would need more information. Does the hagwon allow you to contact other western teachers who have taught there? Would the boss be there when you contact them? Are you getting info on what it's like to teach there? If you can't contact the teachers it's a red flag.
Have you seen the contract? If you have, please read it carefully, and let people on waygook.org review any strange clauses. Are there any strange fees and charges involved? Your contract will give indications of how you'll be treated.
As regards being "North American owned and operated," that can be good, because you may communicate more easily and focus on teaching with few cultural misunderstandings. However, Gangnam is a very competitive area. If the ad stated "North American female only," then that shows the school's priorities. Also, if the teachers all turn out to be beautiful. Gangnam is competitive in that way.
In any case, try to get as much info as possible from the school.