Ponzi scheme, for one (4)
I believe the answer is:
scam
'ponzi scheme for one' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scam that I've seen before include "A slangy swindle or fraud" , "Swindle, fraud (colloq.)" , "fiddle" , "Rip-off" , "rook" .)