Persuading despicable sort to hide diamonds in part of plane (9)
I believe the answer is:
wheedling
'persuading' is the definition.
(wheedling is a kind of persuading)
'despicable sort to hide diamonds in part of plane' is the wordplay.
'despicable sort' becomes 'heel' (I can't explain this - if you can you should believe this answer much more).
'to hide' is an insertion indicator.
'diamonds' becomes 'd' (abbreviation in bridge say).
'in' indicates putting letters inside.
'part of plane' becomes 'wing' (planes have wings).
'heel' placed around 'd' is 'heedl'.
'heedl' put within 'wing' is 'WHEEDLING'.
Can you help me to learn more?
(Other definitions for wheedling that I've seen before include "Buttering up" , "Inveigling, coaxing" .)