Within 1km of Seongsu Station: Daiso Seongsu 2-ga (106 Seongdeokjeong-gil) and

Ttukseom Station Store (6 Achasan-ro), both open until 10 pm, easy after Seongsu's cafés. To try several scents, the Daily Comma Signature Perfume Discovery Set (3.3ml x3) is ₩2,000 with 5.5K+ orders. It's liquid, so use your 1L carry-on bag.