Trader’s ego interrupting upset storyteller (8)
I believe the answer is:
retailer
'trader's' is the definition.
(someone who sells things)
'ego interrupting upset storyteller' is the wordplay.
'ego' becomes 'I' ('I' in Latin).
'interrupting' is an insertion indicator.
'upset' says the letters should be written backwards.
'storyteller' becomes 'relater' (someone relating a story).
'relater' written backwards gives 'retaler'.
'i' going within 'retaler' is 'RETAILER'.
(Other definitions for retailer that I've seen before include "One selling to consumers" , "Merchant" , "Seller to the public" , "story-teller" , "Purveyor" .)