black-market broker
Refers to an intermediary who illegally trades goods, currency, or services outside official channels.
In the chaotic postwar period, black-market brokers sold food and supplies at high prices.
The police arrested a black-market broker who was illegally trading foreign currency.
Compound of 闇 (yami, 'darkness; underground') and ブローカー (broker). The exact origin is uncertain, but it likely emerged in post-WWII Japan to describe illegal intermediaries.