I have a new 400-page book out on South Korean coins and one of the chapters of my book was all about the Bank of Korea mint sets and their historical pricing over the years.
Selling on
ebay is fine, if you don't have access to the Korean coin market.
Mind you, the mint sets that you sell on
ebay will make you a good return, especially if you've had them for a while, but the sets will probably be bought by someone in Korea who could very likely turn around and sell them locally for 2X to 3X the price you sell it for on
ebay.
Those are hot in Korea, although prices have cooled in the last year for some reason.