A bribe? That's a blow! (10)
I believe the answer is:
backhander
I believe this clue is a double definition.
'a bribe?' is the first definition.
(I've seen this before)
'a blow' is the second definition.
(I know that backhander is a type of blow)
'that's' is the link.
(Other definitions for backhander that I've seen before include "Bribe -- a dark bench (anag)" , "sweetener" , "court action" , "Bribe (in court?)" , "Bribe - tennis stroke" .)