I definitely like (1) and (3) best, but they need a little repair work: Either 'A decent man prefers money from a decent source' or 'Decent men prefer money from decent sources'. Either 'A gentleman make his fortune in a decent way' or 'Gentlemen make their fortunes in a decent way'. Or how about: 'A gentleman makes money like a gentleman'-- this one is subtle but effective (maybe).
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