The quote most people would reference is probably this one: People of the same trade seldom meet together, even for merriment and diversion, but the conversati

The quote most people would reference is probably this one: People of the same trade seldom meet together, even for merriment and diversion, but the conversation ends in a conspiracy against the public, or in some contrivance to raise prices. – The Wealth of Nations, Book I, Chapter X.