E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To sweat a client. To make him bleed; to fleece him.
To sweat coin. To subtract part of the silver or gold by friction, but not to such an amount as to render the coin useless as a legal tender. The French use suer in the same sense, as Suer son argent, to sweat his money by usury. Vous faites suer le bonhommetel est votre dire quand vous le pillez. (Harangue du Capitaine la Carbonnade.) (1615.)