Used-car-lot transaction (5-2)
I believe the answer is:
trade-in
'used-car-lot transaction' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for trade-in that I've seen before include "I daren't (anag)" , "Article used in part payment for another" , "Old item given in part payment for a new one" , "Article used in part-exchange" , "Trained (anag.)" .)