Sweetener worker fed to patron (10)
I believe the answer is:
backhander
'sweetener' is the definition.
(I've seen this before)
'worker fed to patron' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'fed to' indicates putting letters inside.
'patron' becomes 'backer' (backer is a kind of patron).
'hand' inserted inside 'backer' is 'BACKHANDER'.
(Other definitions for backhander that I've seen before include "Bribe (in court?)" , "court action" , "Swipe" , "strike" , "sweetener" .)