Curse faulty wares (5)
I believe the answer is:
swear
'curse' is the definition.
(synonyms)
'faulty wares' is the wordplay.
'faulty' indicates an anagram.
'wares' with letters rearranged gives 'SWEAR'.
(Other definitions for swear that I've seen before include "Utter obscenities or take an oath" , "Assert" , "Vow, attest" , "Vow; blaspheme" , "Emit oath or take vow" .)