Sign finally changed hands for scrap (6)
I believe the answer is:
cancel
'scrap' is the definition.
(I've seen this before)
'sign finally changed hands' is the wordplay.
'sign' becomes 'can' (can is a kind of sign).
'finally changed hands' becomes 'cel' (I can't explain this - if you can you should believe this answer much more).
'can'+'cel'='CANCEL'
'for' is the link.
(Other definitions for cancel that I've seen before include "Declare null and void" , "Annul or rescind" , "Rescind, abolish" , "Go for an annulment" , "Call off (arranged event)" .)