Service provider quietly starting fires (6)
I believe the answer is:
parson
'service provider' is the definition.
(I've seen this in another clue)
'quietly starting fires' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'starting fires' becomes 'arson' (illegally starting fires).
'p'+'arson'='PARSON'
(Other definitions for parson that I've seen before include "One with benefice" , "service provider" , "Aprons (anag.)" , "Churchman" , "Minister of religion" .)