Commercial with good tune (6)
I believe the answer is:
adjust
'tune' is the definition.
(I know that tune is a more specific form of the action adjust)
'commercial with good' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'with' is a charade indicator (letters next to each other).
'good' becomes 'just' (synonyms).
'ad'+'just'='ADJUST'
(Other definitions for adjust that I've seen before include "Tune" , "Change slightly to fit" , "Make slight corrections to" , "Correct" , "Adapt (oneself)" .)