carriage trade, n. — Green’s Dictionary of Slang

carriage trade n.

[a hangover f. earlier divisions of transport. Note mid-19C SE carriage company, those who own their own carriage(s); thus the wealthy or upper classes]

the upper classes, usu. used ironically.

1942		R. Chandler High Window 105: ‘It ain’t a lot worse than lots of business personals,’ Breeze said. ‘It don’t seem to be aimed at the carriage trade.’.
1953		R. Chandler Long Good-Bye 95: So I called a man I knew in the Carne Organisation, a flossy agency in Beverly Hills that specialized in protection for the carriage trade.
1973		G.V. Higgins Digger’s Game (1981) 94: Those’re good items, you get the carriage trade with them.
1999		G. Branwyn message to ADS-L 🌐 26 Nov. (Hospital Slang) carriage trade: n having practice restricted to wealthy patients.