Green’s Dictionary of Slang

1. to render oneself gullible, to become a victim.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

2. to make someone into a victim.

1832

Satirist (London) 8 Apr. 119/2: Among the flat-fish of Crockford's [...] Thomas Read Kent Kemp, the M. P. for Lewes, and Lyne Stephens, appear the most gudgeonable.