noun
black marketeer; black market trader
Refers to a person who buys and sells goods illegally, especially during shortages or under price controls.
戦後、多くの闇商人が物資を高値で売っていた。
After the war, many black marketeers sold goods at high prices.
闇市 is the black market itself, while 闇商人 is the person who operates in it.
Compound of 闇 (yami, 'darkness; illegal') and 商人 (shōnin, 'merchant').