Inexorable seller sent out (10)
I believe the answer is:
relentless
'inexorable' is the definition.
(I know that inexorable can be written as relentless)
'seller sent out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'seller'+'sent'='sellersent'
'sellersent' with letters rearranged gives 'RELENTLESS'.
(Other definitions for relentless that I've seen before include "Unyielding - implacable" , "Inexorable" , "Persistent" , "Dogged" , "Oppressively constant; inflexible" .)