German stops dissolute man becoming crook (5)
I believe the answer is:
rogue
'crook' is the definition.
(I know that Rogue has the occupation the thief)
'german stops dissolute man' is the wordplay.
'german' becomes 'g' (abbreviation).
'stops' means one lot of letters goes inside another (stopping can mean blocking a gap).
'dissolute man' becomes 'roue' (I've seen this in another clue).
'g' placed into 'roue' is 'ROGUE'.
'becoming' is the link.
(Other definitions for rogue that I've seen before include "Fraud" , "Bad person" , "Old Greek" , "Stray" , "Scamp" .)