Complex trade involves accessory (5)
I believe the answer is:
extra
'accessory' is the definition.
(I've seen this before)
'complex trade involves' is the wordplay.
'involves' indicates a hidden word.
'EXTRA' is hidden in the letters of 'complex trade'.
(Other definitions for extra that I've seen before include "Minor actor in crowd scene" , "Run; in addition" , "Run scored but not off the bat" , "appearing in crowd scene" , "No great contribution to film" .)