Possibly bitter about everything, commercial singer (9)
I believe the answer is:
balladeer
'singer' is the definition.
(balladeer is a kind of singer)
'possibly bitter about everything commercial' is the wordplay.
'possibly bitter' becomes 'beer' (I've seen this before. I am not sure about the 'possibly' bit.**).
'about' is an insertion indicator.
'everything' becomes 'all' (I've seen this before).
'commercial' becomes 'ad'.
'all'+'ad'='allad'
'beer' placed around 'allad' is 'BALLADEER'.
Can you help me to learn more?
(Other definitions for balladeer that I've seen before include "pop singer" , "One sings" , "One making a song" , "Minstrel" .)