Green’s Dictionary of Slang

sold adj.

[sell v. (1); Partridge notes phr. sold again and got the money as ‘a costermonger’s catch-phrase on having successfully “done” someone in a bargain’]

1. [early 19C+] tricked, fooled.

2. [late 19C+] convinced, successfully persuaded.

In phrases

sold like a bullock in Smithfield (adj.) [Smithfield (founded in the 12C) remains London’s main wholesale meat-market, although live animals have not been brought there since 1855]

[early–mid-19C] badly cheated; utterly betrayed.

sold on (adj.)

[1920s+] convinced, fascinated by.