Sentence:  “... we ain't called on to believe every smooth-talking <WSD>jackleg</WSD> who wanders in here.” 
Meaning of the word marked with <WSD> tags:  A shyster or con artist; a gambler who cheats;<ref>Tom Dalzell (ed.), "The Routledge Dictionary of Modern American Slang and Unconventional English", New York: Routledge, 8th edition, 2009, p. 554.</ref> a generally dishonest or reprehensible person.