Is it rude to tip in Korea?
Not rude, but genuinely unnecessary — and often confusing for the person receiving it. Korea has no tipping culture: restaurant staff, taxi drivers and hotel workers are paid a full wage and the price you see is the price you pay. If you leave cash on a table, a server will usually chase you down the street to return it, assuming you forgot it.
The exceptions are narrow. Hotels aimed at international guests sometimes add a 10% service charge automatically (it'll be printed on the bill). Some tour guides and private drivers who work mainly with foreign tourists have come to expect tips because their customers offer them. Outside those cases, the polite move is simply to say 잘 먹었습니다 (jal meogeotseumnida — "I ate well") on the way out. That lands far better than money.
— KoreaToolkit team, Seoul