Sales campaign conceals dishonest scheme (4)
I believe the answer is:
scam
'dishonest scheme' is the definition.
(I've seen this before)
'sales campaign conceals' is the wordplay.
'conceals' indicates the answer is hidden within the clue.
'SCAM' is hidden within 'sales campaign'.
(Other definitions for scam that I've seen before include "Con trick" , "A modern kind of swindle" , "Swindle (sl.)" , "fiddle" , "Confidence trick, swindle" .)