Green’s Dictionary of Slang

one who swears false oaths for a fee; a perjurer.

1747		Life and Character of Moll King 12: harry: But who had you in your Ken last Darkee? moll: We had your Dudders and your Duffers, Files, Buffers, and Slangers. [Ibid.] 24: Buffers, Affidavit-Men.
a.1790		H.T. Potter New Dict. Cant (1795).
1811		Lex. Balatronicum.
1827		Commercial Advertiser (N.Y.) 1 Feb. 2/3: The buffer demanded twelve benders, which was more than the whole five owned, but [they] promised to go and satisfy the party, and they departed apparently contented with a night’s lark.
1834		‘The Small-Coal Man’ in London Eve. Standard 22 Dec. 4/4: Ye Buffer boys and varmint blades, / Vot follows up no rig’lar trades.
1835		G. Kent Modern Flash Dict. n.p.: Buffer, a perjurer.
1846		Bell’s Life in Sydney 5 Sept. 2/4: Clinton, the fellow who gets assaulted oftener than all the police put together, appeard as a hearty buffer and jealous jackall to swear that he saw one Charlotte Hayes [etc.].
1848		Flash Dict. in Sinks of London Laid Open We have already mentioned his peculiar forte at picking up jewelry from [...] school-girls. We will now enter [...] upon his capabilities as a full-blooded buffer.
1854		Life in Boston & N.Y. (Boston, MA) 13 May n.p.:
1859		Hotten Dict. of Modern Sl. etc. 13: BUFFER [...] the term was once applied to those who took false oaths for a consideration.
1859		Matsell Vocabulum 15: buffet [sic]. A false swearer.
1881		Trumble Sl. Dict. (1890).
1895		Crowe Aus. Sl. Dict. 12: Buffer, a [...] perjurer.
1899		Aberdeen Press 21 June 7/5: The resurrection man and the buffer conveyed the body to a species of outhouse, which the surgeon [...] devoted to the purpose of dissection.
1901		Argus (Melbourne) 20 Sept. 6/4: If his buffer or professional perjurer cannot prove an alibi, [he] may in due course be fitted, or found guilty.