Advertise post, a dishonest scheme (3-2,3)
I believe the answer is:
put-up job
'a dishonest scheme' is the definition.
(I've seen this before)
'advertise post' is the wordplay.
'advertise' becomes 'put up' (as in putting up a sign).
'post' becomes 'job' (I've seen this before).
'putup'+'job'='PUT-UP JOB'
(Other definitions for put-up job that I've seen before include "Dishonest scheme" , "Prearranged underhand deceitful enterprise" , "Deception arranged in advance" , "sham!" , "Prearranged scam" .)