Check polish once more (6)
I believe the answer is:
rebuff
This clue is a double definition.
'check' is the first definition.
(I've seen this before)
'polish once more' is the second definition.
('buff' is an answer for 'polish' so perhaps 'rebuff' is OK for 'polish once more')
(Other definitions for rebuff that I've seen before include "Reject bluntly" , "Reject in an ungrateful manner" , "Reject abruptly" , "Snub, blunt refusal" , "Deliberate discourteous act" .)