Rate fixed by more reliable financial officer (9)
I believe the answer is:
treasurer
'financial officer' is the definition.
(synonyms)
'rate fixed by more reliable' is the wordplay.
'fixed' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'more reliable' becomes 'surer' ('sure' can be similar in meaning to 'reliable').
'rate' is an anagram of 'trea'.
'trea'+'surer'='TREASURER'
(Other definitions for treasurer that I've seen before include "Finance officer" , "Fiscal officer" , "Society official" , "Book-keeper" , "Committee member" .)