Promoter travels by ship, it's said, to island (8)
I believe the answer is:
salesman
'promoter' is the definition.
(someone who promotes a product)
'travels by ship it's said to island' is the wordplay.
'travels by ship' becomes 'sails' (travels in a boat with sails).
'it's said' shows a homophone (sound like).
'to island' becomes 'man' (the Isle of Man is an example).
'sails' is a homophone of 'sales'.
'sales'+'man'='SALESMAN'
(Other definitions for salesman that I've seen before include "Amen, lass, to the seller" , "He's a seller" , "Male shopworker" , "He sells lean mass, oddly" , "Death of a . . . . . . . . (Arthur Miller) (8)" .)