Be successful in swindle (3)
I believe the answer is:
win
'be successful' is the definition.
(I've seen this before)
'in swindle' is the wordplay.
'in' indicates the answer is hidden within the clue.
'WIN' is hidden in the letters of 'swindle'.
(Other definitions for win that I've seen before include "Come first" , "Succeed, conquer" , "Achieve victory" , "Finish in first place" , "Be victorious or succeed" .)