DAB,
expert, well vers'd in Roguery. A Rum Dab, a very dextrous Fellow at Thieving, Cheating, Sharping, &c.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Dab in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).