Work to support quiet retail outlet (4)
I believe the answer is:
shop
'retail outlet' is the definition.
(I've seen this before)
'work to support quiet' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'to support' is a charade indicator (letters next to each other) (in a down clue, some letters hold others up).
'quiet' becomes 'sh'.
'op' after 'sh' is 'SHOP'.
(Other definitions for shop that I've seen before include "Inform on (slang)" , "Place to buy" , "Sell" , "Emporium" , "Retail establishment" .)