Fraudulent scheme? Clear off — not right! (4)
I believe the answer is:
scam
'fraudulent scheme?' is the definition.
(I've seen this in another clue)
'clear off not right' is the wordplay.
'clear off' becomes 'scram' (both can be used to tell someone to go away).
'not' indicates named letters should be taken away.
'right' becomes 'r' (common abbreviation).
'scram' with 'r' taken away is 'SCAM'.
(Other definitions for scam that I've seen before include "A slangy swindle or fraud" , "Fraudulent action" , "rook" , "Fraud, dishonest scheme" , "ploy" .)