Rogue trader's modest about fancy bow (6)
I believe the answer is:
cowboy
'rogue trader's' is the definition.
(both can mean an unscrupulous trader)
'modest about fancy bow' is the wordplay.
'modest' becomes 'coy' (I've seen this before).
'about' indicates putting letters inside.
'fancy' indicates an anagram.
'bow' anagrammed gives 'wbo'.
'coy' enclosing 'wbo' is 'COWBOY'.
(Other definitions for cowboy that I've seen before include "Wild West character" , "Mounted herdsman" , "Wrangler" , "Cattle herder of the American wild west" , "Hired hand who tended cattle in the old west" .)