Cancel agent deal, losing face (6)
I believe the answer is:
repeal
'cancel' is the definition.
(I know that repeal is a more specific form of the action cancel)
'agent deal losing face' is the wordplay.
'agent' becomes 'rep' (short for representative).
'losing face' means to remove the first letter.
'deal' with its first letter removed is 'eal'.
'rep'+'eal'='REPEAL'
(Other definitions for repeal that I've seen before include "Abrogate" , "Revoke, a law say" , "'Annul, revoke (6)'" , "Annulment" , "Countermand" .)