Double-cheat without even being sweet (6)
I believe the answer is:
dulcet
'being sweet' is the definition.
('dulcet' can be a synonym of 'sweet')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for dulcet that I've seen before include "Sweet-sounding, melodious" , "(Of sound) sweet and soothing" , "Of voice or tone, sweet-sounding" , "(Of sound) melodious" , "Sweet, gentle (tones)" .)