What you are trying to do is called arbitrage is trading which is trying to make a profit by finding the price difference between two platforms and it is profitable whenever that difference is found and it is not related to Korea.
Arbitrage is trading that exploits the tiny differences in price between identical assets in two or more markets
Source --->
https://www.investopedia.com/terms/a/arbitrage.asp#:~:text=Arbitrage%20is%20trading%20that%20exploits,difference%20between%20the%20two%20prices.
As for the reason for Korea, it is either the time difference or the difference in trading volumes.
- Is this type of trading guaranteed profit??
We cannot be certain of yes, the price of Bitcoin is variable and a difference of 6-7% may occur within a short time, and therefore the faster your trading and on reliable platforms, the more guaranteed the profit, but less return.
So we can't consider it $100 guaranteed.
+ this is for Bitcoin and top 10 cryptos and not guaranteed for altcoins.