Quiet salesperson, a socialist, getting ready (8)
I believe the answer is:
prepared
'ready' is the definition.
(similar in meaning)
'quiet salesperson a socialist' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'salesperson' becomes 'rep' (sales rep).
'socialist' becomes 'red' (red can informally mean a socialist).
'p'+'rep'+'a'+'red'='PREPARED'
'getting' acts as a link.
(Other definitions for prepared that I've seen before include "Made or got ready" , "edited" , "Waiting" , "Ready for action" , "All set" .)