Illegal trade in cars? (7)
I believe the answer is:
traffic
This clue could be a double definition.
'illegal trade' is the first definition.
'traffic' can be an answer for 'trade' (I've seen this before). I'm unsure of the 'illegal' bit.
'cars?' is the second definition.
'in' is the link.
Can you help me to learn more?
(Other definitions for traffic that I've seen before include "dealings" , "that may be in jam?" , "Illegal trading" , "Movement of vehicles" , "Communications" .)