Green’s Dictionary of Slang

a customs house clerk.

1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Damned Soul. A clerk in a counting house, whose sole business it is to clear or swear off merchandise at the custom-house; and who, it is said, guards against the crime of perjury, by taking a previous oath, never to swear truly on those occasions.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.