A shopkeeper sounded more offensive (7)
I believe the answer is:
grosser
'more offensive' is the definition.
('gross' can be similar in meaning to 'offensive')
'a shopkeeper sounded' is the wordplay.
'a shopkeeper' becomes 'grocer' (I've seen this before).
'sounded' indicates a 'sounds like' (homophone) clue.
'grocer' sounds like 'GROSSER'.
(Other definitions for grosser that I've seen before include "More corpulent" , "more vulgar" .)