The shopkeeper sounds coarser (7)
I believe the answer is:
grosser
'coarser' is the definition.
('gross' can be a synonym of 'coarse')
'the shopkeeper sounds' is the wordplay.
'the shopkeeper' becomes 'grocer' (I've seen this before).
'sounds' indicates a 'sounds like' (homophone) clue.
'grocer' is a homophone of 'GROSSER'.
(Other definitions for grosser that I've seen before include "more vulgar" , "More corpulent" .)