Bargain fasteners returned (4)
I believe the answer is:
snip
'bargain' is the definition.
(slang term for a good deal)
'fasteners returned' is the wordplay.
'fasteners' becomes 'pins' (pin is a kind of fastener).
'returned' shows that the letters should be reversed in order.
'pins' reversed gives 'SNIP'.
(Other definitions for snip that I've seen before include "Cut - certainty" , "Easy to do - use pins" , "Something cheap or easy to do" , "Cut back" , "Steal" .)