noun
scalper; ticket tout
Slang term for someone who resells tickets at inflated prices, especially near venues. Derived from reversing the syllables of ふだ (札, ticket).
See also: 札 (ふだ)
コンサート会場の近くでダフ屋がチケットを売っていた。
A scalper was selling tickets near the concert venue.
ダフ屋からチケットを買うのは違法になることがある。
Buying tickets from a scalper can be illegal.
From reversing the syllables of ふだ (札, ticket) to だふ, plus 屋 (dealer). The exact origin is uncertain, but it is a well-known piece of Japanese slang.