Rebuke salesman over cover (7)
I believe the answer is:
reproof
'rebuke' is the definition.
('reproof' can be a synonym of 'rebuke')
'salesman over cover' is the wordplay.
'salesman' becomes 'rep' (I've seen this before).
'over' means one lot of letters go next to another.
'cover' becomes 'roof' (roofing is a kind of covering**).
'rep'+'roof'='REPROOF'
(Other definitions for reproof that I've seen before include "Ticking-off" , "Criticism" , "Blaming" , "Ticking off" , "Castigation" .)