One who foretells financial advantage for the auditor (7)
I believe the answer is:
prophet
'one who foretells' is the definition.
'financial advantage for the auditor' is the wordplay.
'financial advantage' becomes 'profit' (I've seen this before).
'for the auditor' indicates a 'sounds like' (homophone) clue.
'profit' is a homophone of 'PROPHET'.
(Other definitions for prophet that I've seen before include "Religious leader" , "Augur" , "Divine spokesman or forecaster" , "One who predicts the future" , "Oracle" .)