Salesperson encountered rising anger (6)
I believe the answer is:
temper
'anger' is the definition.
(I know that temper is a type of annoyance)
'salesperson encountered rising' is the wordplay.
'salesperson' becomes 'rep' (sales rep).
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'rising' shows that the letters should be reversed in order (going up in a down clue).
'rep'+'met'='repmet'
'repmet' written backwards gives 'TEMPER'.
(Other definitions for temper that I've seen before include "Volatile anger - don't lose it" , "Fit of anger - don't lose it" , "Angry state of mind" , "Frame of mind" , "Bad humour" .)