Illegal trade (5,6)
I believe the answer is:
black market
'illegal trade' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for black market that I've seen before include "Dodgy dealing" , "Selling in violation of controls" , "Place to purchase illicit goods" , "Covert trade in illicit goods" , "Illegal system of trade" .)