Starts to trade on your sweet trifles (4)
I believe the answer is:
toys
'trifles' is the definition.
(I've seen this before)
'starts to trade on your sweet' is the wordplay.
'starts to' says to take the initial letters.
The initial letters of 'trade on your sweet' is 'TOYS'.
(Other definitions for toys that I've seen before include "Children's playthings" , "Sports" , "Plays (with something), not seriously" , "Chihuahuas?" , "Film" .)