Transgression of dodgy dealer (7)
I believe the answer is:
offence
'transgression' is the definition.
(I know that offence is a type of transgression)
'of dodgy dealer' is the wordplay.
'dodgy dealer' becomes 'fence' (trader of stolen goods).
'of'+'fence'='OFFENCE'
(Other definitions for offence that I've seen before include "Breach of conduct" , "Attack - crime" , "Misdemeanour" , "Criminal action" , "illegality" .)