After immigration and baggage claim, customs is a separate step. Korea Customs Service currently states a basic tax-exemption allowance of US$800 for ordinary traveler goods, with separate rules for categories such as alcohol, tobacco and perfume. Goods above the allowance, commercial goods, restricted items and certain agricultural, animal or plant products must be declared.
The current customs guidance also lists payment instruments exceeding the equivalent of US$10,000 among items that require declaration. If you are unsure whether an item is restricted or declarable, declare it and ask customs rather than assuming a duty-free-shop purchase is automatically exempt.
One important caution: official Korea Customs pages currently show inconsistent perfume allowance figures on different pages. Because of that conflict, this guide deliberately does not state a fixed perfume quantity. Recheck the current traveler declaration page on the day you travel.
Korea Customs states that voluntary declaration of goods above the allowance can receive a reduction in the standard customs duty, while failure to declare can trigger additional tax. Keep receipts for high-value purchases and make the decision before entering the Nothing to Declare channel.