Green’s Dictionary of Slang

1. a criminal beggar who wanders the country, selling goods that have supposedly been smuggled through the customs; thus capitalizing on the greed and gullibility of their provincial customers. The clandestine style of their encounter with a customer gives the synon. whispering dudder.

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: Dudders, Fellows that sell Spital-fields Handkerchiefs for India ones.
1753		J. Poulter Discoveries (1774) 30: The Dudders; that is, Sellers of Handkerchiefs. [Ibid.] 34: Dudders [...] are a Set of People that resort to Fairs and Markets, under Pretence of being Smugglers, and selling nothing but prohibited Goods; at the same time they are ordinary Goods made in England.
1781		G. Parker View of Society II 158: Sham Leggers. The Duff. Whispering Dudders. These are divided into several classes: some travel on horseback, and some on foot; some with carts and waggons, &c. They frequent the out-skirts of cities, large towns, markets, villages, and fairs. The goods they have for sale are damaged, which they get from on board ships or out of large manufactories; but tho’ damaged, they are generally of the newest fashions and neatest patterns. [...] They endeavour to make you believe that the goods they sell are smuggled, tho’ they were really manufactured in Spitalfields.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Dudder, or Whispering Dudder. Cheats who Travel the Country, pretending to sell Smuggled Goods & accost their intended Dupes in a whisper. The Goods they have for sale are Damaged; purchased by them out of large manufactories.
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859, 1860		Hotten Dict. of Modern Sl. etc.
1864, 1867, 1870		Hotten Sl. Dict.
1884		‘Career of a Scapegrace’ in Leicester Chron. 10 May 12/1: A ‘dudder,’ a type of travelling hawker now seldom seen, except in remote parts of the country — a knavish packman, who professed to go in fear of the excise man, and sold his cheap French silk handkerchiefs [...] for quadruple their real value.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxiv 4/4: dudder: A seller of shoddy goods. A person selling legitimately purchased goods as being stolen property to make sales easier.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 24: Dudder Seller of phoney goods.

2. (Aus. Und.) one who sells fake narcotics.

1931

Eve. News (Rockhampton, Qld) 27 May 3/1: A ‘dudder’ is a person who passes off some powder as cocaine or morphine.