Green’s Dictionary of Slang

buffer n.2

also buffet
[buff v.1 ]

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

[UK]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.
[UK]H.T. Potter New Dict. Cant (1795).
[UK]Lex. Balatronicum.
[US]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.
[UK]‘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.
[UK]G. Kent Modern Flash Dict. n.p.: Buffer, a perjurer.
[Aus]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.].
[UK]Flash Dict. in Sinks of London Laid Open.
[UK]Hotten Dict. of Modern Sl. etc. 13: BUFFER [...] the term was once applied to those who took false oaths for a consideration.
[US]Matsell Vocabulum 15: buffet [sic]. A false swearer.
[US]Trumble Sl. Dict. (1890).
[UK]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.