Green’s Dictionary of Slang

1. the gold pieces that are used to trap the victim in a money-switching fraud.

1608

Dekker Lanthorne and Candle-Light Ch. 11: This Art or slight of changing Gold into Siluer, is called Trimming [...] The Gold which they bring to the Cittizen, is cald Iasons Fleece.

2. a citizen who has been swindled of their money.

c.1698		B.E. Dict. Canting Crew n.p.: Jason’s fleece c. a Citizen cheated of his Gold.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.