Piece of marketing understated in part (3)
I believe the answer is:
gun
'piece' is the definition.
(I've seen this before)
'of marketing understated in part' is the wordplay.
'of' indicates the answer is hidden within the clue.
'GUN' is hidden within 'marketing understated part'.
(Other definitions for gun that I've seen before include "Platform from which to shoot" , "What has barrel" , "Shooter" , "Artillery piece" , "Firearm" .)