Nothing in shops is sent back dirty (6)
I believe the answer is:
soiled
'dirty' is the definition.
(soiled can mean dirty or stained)
'nothing in shops is sent back' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'in' is an insertion indicator.
'shops' becomes 'delis' (deli is a kind of shop).
'is sent back' is a reversal indicator.
'o' placed into 'delis' is 'delios'.
'delios' written backwards gives 'SOILED'.
(Other definitions for soiled that I've seen before include "Stained and dirty" , "Dirtied" , "Dirty, grimy" , "Made dirty" .)