Green’s Dictionary of Slang

1. a villain who kills healthy horses and sells the skins; also a dog-thief.

c.1698		B.E. Dict. Canting Crew n.p.: Buffer, c. a Rogue that kills good Horses, only for their Skins, by running a long Wyre into them, and sometimes knocking them on the Head, for the quicker Dispatch.
1725		New Canting Dict.
1737		Bacchus and Venus n.p.: Buffer, a rogue that killed good sound horses for the sake of their skins, by running a long wire into them [F&H].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict.
1749		B.M. Carew ‘The Oath of the Canting Crew’ in Farmer Musa Pedestris (1896) 51: No ballad-basket, bouncing buffer, / Nor any other, will I suffer.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: buffer, one that steals and kills horses and dogs for their skins.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1848		G.W.M. Reynolds Mysteries of London I.
1859		Hotten Dict. of Modern Sl. etc. 13: In 1737, a buffer was a ‘rogue that killed good sound horses for the sake of their skins, by running a long wire into them.’ — Bacchus and Venus.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.

2. (also buffor) a villain, specializing in selling supposedly smuggled goods; thus buff it, to peddle such articles.

1760		‘Come All You Buffers Gay’ in Farmer Musa Pedestris (1896) 52: Come all you buffers gay, / That rumly do pad the city.
1818		W. Perry London Guide 2: Fellows who hang about in inn yards [...] selling and buying some article [are] called ‘Duffors or Buffors’.
1818		W. Perry London Guide 91: Buffers [...] are invariably north-country-men. Jordaine was a Glasgow man and made ten thousand pounds [...] but never buffed it in the streets of London.
1821		‘An Amateur’ Real Life in London I 169: Buffers miscalled Duffers—[...] go about from house to house, and attend public-houses, inns, and fairs, pretending to sell smuggled goods.
1836		Comic Almanack Feb. 47: Come, buffers and duffers, and dashers and smashers.
1859		‘Hundred Stretches Hence’ in Matsell Vocabulum 124: And where the buffer, bruiser, blowen, / And all the cops and beaks so knowin’.
1865		Plymouth Wkly Democrat (IN) 5 Jan. 1/5: Horse jockies, horse thieves [...] buffers, bummers [...] bravos and panderers [...] bludgenors, bounty jumpers, koniackers, knucks [and] pocketbook stuffers.