I use a tailor in HKG (Danny's by the Sheraton) as I have been going there for yours -- excellent quality and price. Seoul has very stylish clothes -- people spend lavishly on 2 things, cars and clothes ... as housing is sooooo expensive they will never be able to afford it. Thus there is a lot of clientele for well made and stylish clothes. I would have no hesitation in using a tailor in Seoul (whereas I don't in Bangkok, India or even Singapore -- at least not for a semi-random choice!).