Restrain salesman on ship (7)
I believe the answer is:
repress
'restrain' is the definition.
(thesaurus)
'salesman on ship' is the wordplay.
'salesman' becomes 'rep' (I've seen this before).
'on' becomes 're' ('on' can be mean 'with reference to').
'ship' becomes 'ss'.
'rep'+'re'+'ss'='REPRESS'
(Other definitions for repress that I've seen before include "Curb" , "Silence" , "Check" , "bottle up" , "Subdue" .)