Forty years ago, the richest professors at some of the world's great universities were the art historians, who were paid to certify that some painting a dealer had for sale was indeed a Rembrandt or a Rubens or a Raphael. Their fees were a percentage of the sale price of the painting. If they said it was genuine, they got paid a lot; if they said it was the work of a lesser artist (or a fake), they got paid very little. Villa I Tatti, art historian Bernard Berenson's great estate near Florence, stands as evidence of how lucrative such commissions were.

The favourable opinion that enriched a professor also enriched an art dealer. Indeed, it could be argued, and was argued, that the purchaser—whose money was divided among seller, dealer and expert—lost nothing, because what he then hung on his wall was a certified masterpiece.

Those old days in the art market are the proper reference for the latest Wall Street scandal: the analysts whose pay is linked to the banking business their firm does with companies whose stock the analysts recommend to the firm's brokerage customers.

This perverse incentive in finance was created when the individual who links the brokerage client to the markets became a "registered representative"— someone who works for the firm—rather than, as he had been, "a customer's man": someone whose job was to care for the interests of the client.

From the firm's point of view, the defect of the customer's man was that he could take his customers with him. In the 1970s, when the brokerage houses became corporations that had to sell their own stock, they needed a structure that tied the client to the firm. They wrote non-compete clauses into employment contracts and sometimes went so far as to sue a registered rep whose clients followed him to another firm. And they demanded that the rep declare a first loyalty to his employer rather than to his customer. In practice, this meant a willingness to tout the stocks and bonds the employer was underwriting or distributing from its own trading inventory, regardless of personal views of their value.

It was only a short step from rewarding the registered rep for his sales of the firm's Rembrandts to rewarding the research analyst for the report that echoed the wish-lists of corporate executives choosing dealers for their own Rembrandts. From that, much harm has followed.

The work of brokers is to resolve the conflicts of interest between sellers and buyers, in a fair and honest way. There has always been an element of doubt that brokers could maintain these standards if they were also dealers whose profit depended on having the client pay more.

Writing the Securities Acts in the 1930s, Congress asked the new Securities and Exchange Commission to explore conflicts of interest in the broker/dealer combination. The SEC staff reported in 1935 that separation was feasible and probably desirable but the Commission decided instead to raise Chinese walls between the banking and brokerage areas of securities firms.

As a way to keep information confidential in departments of the firm, Chinese walls never worked - the cant line on the street was that "grapevines grow over Chinese walls". But they at least expressed the industry's recognition that a financial firm has obligations to its clients as well as to its own bottom line. Compensating analysts on the basis of the banking business that they attract knocks a big hole in the wall.

What put a stop to the swindle in the art market was a combination of publicity and the disgust of a new generation of art historians, most of whom were not on the gravy train. Today, a historian asked to authenticate will be paid the same fee whether it is thumbs up or thumbs down. Unfortunately, because everybody is in the game, professional discipline will not do it for Wall Street, though publicity helps and many analysts, having worked hard for their degree as chartered financial analyst, are unhappy about the disrespect.

Securities regulation in the US was pioneered by the states, which still have so-called blue-sky laws (to prevent stockbrokers from selling people the blue sky). These laws survive, mostly to give state officials tools against fraudsters who operate locally and never register with the self-regulatory organisations that police the established markets for the SEC.

But if famous brokers sell the blue sky to their customers, they violate state as well as federal law. Eliot Spitzer, New York attorney-general, was well within his competence when he went after Merrill Lynch for inducing analysts to help registered reps sell the securities of companies that gave Merrill banking business, even when the analysts thought the stock was garbage.

Merrill's subsequent settlement with Mr. Spitzer suggests that, just as there was a purge in the art market 40 years ago, Wall Street will undergo a similar clear-out tomorrow.