Green’s Dictionary of Slang

1. a bargain in which the buyer is cheated.

1773		Foote The Bankrupt II i: You deposit so much money, and he grants you such an annuity; a mere Smithfield bargain, that is all.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Smithfield Bargain. A bargain whereby the purchaser is taken in. This is likewise frequently used to express matches or marriages contracted solely on the score of interest, on one or both sides, where the fair sex are bought and sold like cattle in Smithfield.
1790		Oxford Jrnl 11 Dec. 1/1: From the intimate Connection there is, and shouild be, between the Company and Government, it is to the Interest of both not to drive a Smithfield Bargain.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1849		Hertford Mercury 22 Dec. 4/1: A Smithfield bargain is necessarily a gambling transaction, since it always invoves risking the chance of a toss-up.

2. a marriage of convenience, based on financial interest.

1663		J. Wilson Cheats V v: Your daughter has married a gentleman. Is this not better than a Smithfield bargain—give me so much money, and my horse shall leap your mare.
1700		T. Brown Amusements Serious and Comical in Works (1744) III 54: By the procurement of these experienced matrons, a marriage is struck up like a Smithfield bargain.
1709		‘Phoebe Crackenthorpe’ Female Tatler (1992) (43) 98: They abhorred Smithfield bargains.
1721		Penkethman’s Jests 76: Is it possible, says a Gentleman to his Friend, who was going to make a Smithfield Bargain, you can value a Woman that’s to be bought?
[1730		J. Miller Humours of Oxford IV ii: When People are jocky’d into one another in your Smithfield manner, ’tis no wonder they often repent of their Bargain].
1730		Caledonian Mercury 12 Nov. 3/1: The Vulgar Method of making Love, is by acquainting the Lady or her Relations with the situation of our Affairs [...] with this Proviso, always that her Fortune be equivalent [...] under the name of a Smithfield Bargain.
1753		Richardson Sir Charles Grandison (1812) VI 467: The hearts of us women when we are urged to give way to a clandestine and unequal address [...] are apt, and are pleaded with, to rise against the notions of bargain and sale. Smithfield bargains you Londoners call them.
1775		Sheridan Rivals (1776) V i: Why, is it not provoking? when I thought we were coming to the prettiest distress imaginable, to find myself made a mere Smithfield bargain of at last.
1788, 1796		see sense 1.
1802		Morn. Post (London) 26 Feb. 3/1: The Highgate Apothecary, who courted Miss Mellish, knowing that some of her name are eminent carcase butchers, thought it quite in the family way to drive a Smithfield bargain.
1815		Hereford Jrnl 19 July 3/4: Smithfield Bargain [...] the intention of these disgusting bargains is to deprive the husband of any right of prosecution for damages.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1833		Oxford Jrnl 21 Dec. 3/4: The foolish vulgarity of being said to have ‘married well’ [...] the usual mode of doing which is coarsely, and not unaptly, called ‘a Smithfield bargain’.
1881		in Davies Supplement Gloss. [F&H].

an inferior horse which has been smartened up to deceive a prospective buyer; in ext. use, a prostitute.

[1593		Passionate Morrice (1876) 83: It is more vncertaine to know now a daies whether a woman bee honestly modest, or knauishly coye, than whether a Smith-feelde horse will proue good or iadish].
1675		Wycherley Country-Wife I i: That grave circumspection in marrying a country wife is like refusing a deceitful pampared Smithfield jade.