Act as salesman with grudge (9)
I believe the answer is:
represent
'act' is the definition.
(I know that act can be written as represent)
'salesman with grudge' is the wordplay.
'salesman' becomes 'rep' (sales rep).
'with' means one lot of letters go next to another.
'grudge' becomes 'resent' (I've seen this before).
'rep'+'resent'='REPRESENT'
'as' acts as a link.
(Other definitions for represent that I've seen before include "Serve as a symbol for" , "show" , "Portray" , "Explain" , "declare" .)