"Some doctors choose to specialise in diseases of the rich"

More seriously, paying clients are a good thing and selecting for those that afford something is not unreasonable (although glove makers and cobblers for the Georgian and Victorian era wealthy often went broke as the upper class often refused to pay).

Don't discount familiarity with the finances of millionaires by other mean, when I worked in mineral and energy intelligence the bulk of our clients were wealthy enough to discount all IPO's below 50 million as "small beer".