Fixes up cut (4)
I believe the answer is:
snip
'cut' is the definition.
(snip is a kind of cut)
'fixes up' is the wordplay.
'fixes' becomes 'pins' (pinning is a kind of fixing).
'up' is a reversal indicator (in down clue: letters go upwards).
'pins' backwards is 'SNIP'.
(Other definitions for snip that I've seen before include "Surprisingly cheap item" , "Cut with scissors in small strokes" , "Cut with scissors - bargain" , "Cut - certainty" , "Steal" .)