Salesman with attitude has to get better (6)
I believe the answer is:
repair
'to get better' is the definition.
(repair can mean to improve or get better)
'salesman with attitude' is the wordplay.
'salesman' becomes 'rep' (sales rep).
'with' is a charade indicator (letters next to each other).
'attitude' becomes 'air' (I've seen this before).
'rep'+'air'='REPAIR'
'has' acts as a link.
(Other definitions for repair that I've seen before include "retire" , "Travel or proceed toward some place" , "Fix, mend" , "Restore to working order" , "Withdraw" .)