live by your wits
From Longman Dictionary of Contemporary Englishlive by your witslive by your witsDISHONESTto get money by being clever or dishonest, and not by doing an ordinary job → liveExamples from the Corpuslive by your wits• The city's homeless live completely by their wits.• Days when there were no news sensations the newsboys lived by their wits.• Freddie lived by his wits and he was involved with many shady characters.