Keener criminal further up the scale (7)
I believe the answer is:
sharper
I believe this clue is a triple definition!
'keener' is the first definition.
('sharp' can be similar in meaning to 'keen')
'criminal' is the second definition.
(a sharper is someone who cheats at cards)
'further up the scale' is the third definition.
(further up a musical scale)
(Other definitions for sharper that I've seen before include "More acerbic" , "showing greater astuteness" , "Swindler (at cards)" , "More keen or bitter" , "More acute" .)