Dash back with German article for part-exchange (5-2)
I believe the answer is:
trade-in
'part-exchange' is the definition.
(I've seen this before)
'dash back with german article' is the wordplay.
'dash' becomes 'dart' (synonyms).
'back' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'german article' becomes 'ein' (German indefinite article).
'dart' backwards is 'trad'.
'trad'+'ein'='TRADE-IN'
'for' is the link.
(Other definitions for trade-in that I've seen before include "I daren't (anag)" , "Article used in part payment for another" , "Article used in part-exchange" , "Older article used in part payment to retailer" , "Trained (anag.)" .)