Restrain salesperson on about ship (7)
I believe the answer is:
repress
'restrain' is the definition.
(thesaurus)
'salesperson on about ship' is the wordplay.
'salesperson' becomes 'rep' (sales rep).
'on' is a charade indicator (letters next to each other).
'about' becomes 're' ('re' means regarding or about).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'rep'+'re'+'ss'='REPRESS'
(Other definitions for repress that I've seen before include "Curb" , "Keep in subjection" , "Forcibly keep down" , "Check" , "bottle up" .)