Responsibility to deliver cut-price merchandise (4-4)
I believe the answer is:
duty-free
'cut-price merchandise' is the definition.
(as in duty-free items at an airport)
'responsibility to deliver' is the wordplay.
'responsibility' becomes 'duty' (synonyms).
'to deliver' becomes 'free' (I've seen this before).
'duty'+'free'='DUTY-FREE'
(Other definitions for duty-free that I've seen before include "No tax payable as in airports" , "Exempt from import levy" , "without obligation?" , "Not subject to tax, as at airports" , "Non-taxable (imports)" .)