I'm back to inviting readers to submit quotations whose origins they want me to try to trace, using my book, The Yale Book of Quotations, and my more recent researches.
Alicia Calzada asked:
Let me know if you have any luck with this one: 'Never argue with a man who buys ink by the barrel' It has been credited in case law to both Mark Twain and publicist William I. Greener, Jr. Brown v. Kelly Broad. Co., 48 Cal. 3d 711, 744 (Cal. 1989) crediting Twain as the source of the famous adage; State ex rel. Plain Dealer Publ’g Co. v. Geauga Cty. Court of Common Pleas, Juv. Div., 90 Ohio St. 3d79,89 (Pfiefer, J., dissenting) ('The majority has elevated Greener’s law' (‘Never argue with a man who buys ink by the barrel")')
It has also been credited as undetermined, which I think is most accurate: Ralph Keyes, the quote verifier: who said what, where and when 64. The Mark Twain House in Connecticut has no record of Twain saying the phrase.