Green’s Dictionary of Slang

a seller of second-rate goods at very low prices.

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.: Leggers Sham Leggers. Cheats who impose on the Ignorant by pretending to sell them Smuggled Goods but which are in reality old & Dammaged Shopkeepers.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Sham leggers; cheats who pretend to sell smuggled goods, but in reality only deal in old shop-keepers or damaged goods.
1811		Lex. Balatronicum [as cit. 1788].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1788].
1859		Matsell Vocabulum.