Green’s Dictionary of Slang

needles and buttons and other small wares carried by a street-hawker; thus snell-fencer, a hawker of such items.

1873		Sl. Dict. 299: Snell-fencer a street salesman of needles. snells are needles.
1886		W. Newton Secrets of Tramp Life Revealed 10: Snells ... Needles. [Ibid.] 16: Many of this class will make as much as will purchase a ‘Stiff,’ or license, and stock of ‘snells,’ or buttons, needles, &c.
1891		F.W. Carew Autobiog. of a Gipsey 415: Alf Palmer – a chiv, blink, and snell-fencer.