Green’s Dictionary of Slang

(US Und.) to sell brass or galvanized copper watches as ‘gold’ ones; often as stuffing/watch-stuffing n.; thus stuffer/watch-stuffer n., a person who does this; stuff cover n., his assistant.

1839		N.Y. Daily Express 16 May 2/3: Stuffing — which means selling brass watches, pretending them to be gold ones.
1845		Nat. Police Gaz. (NY) 13 Dec. 133/3: On going down Broadway [...] he was accosted by a watch stuffer who, with the assistance of his pal or capper, endevoured to stuff him with a mock watch.
1848		Ladies’ Repository (N.Y.) Oct. VIII:37 317/1: Stuff, To sell articles for what they are not, such as galvanized copper watches for gold, &c. Stuff Cover, a man who assists the stuffer, by introducing himself as a stranger to both parties, and praising the articles to be sold. Stuffer, one who stuffs.
1856		G.G. Foster N.Y. by Gas-Light (1990) 85: The watch-stuffer, the green-horn, the blackleg and the clerk.
1860		Atlantic Monthly Dec. 671: Dog-smudging, ring-dropping, watch-stuffing [...] are all terms which have more or less outgrown the bounds of their Alsatia of Thieves’ Latin and are known of men [DA].