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