Buy and sell vehicles (7)
I believe the answer is:
traffic
I believe this is a double definition.
'buy and sell' is the first definition.
(thesaurus)
'vehicles' is the second definition.
(I've seen this before)
(Other definitions for traffic that I've seen before include "Illegally push" , "Vehicle flow" , "Trade (in cars?)" , "dealings" , "Communications" .)