Cunning good-looker, wicked inside (8)
I believe the answer is:
devilish
'cunning' is the definition.
'good-looker wicked inside' is the wordplay.
'good looker' becomes 'dish' (I've seen this in other clues).
'wicked' becomes 'evil' (similar in meaning).
'inside' is an insertion indicator.
'dish' going around 'evil' is 'DEVILISH'.
(Other definitions for devilish that I've seen before include "Very difficult to deal with" , "Diabolical" , "Mischievous; rakish" , "naughty" , "Very wicked" .)