TRUST is the bedrock of business everywhere, but the sources from which it springs are different. In Japan, where reputation and relationships are considered precious, the informal cues are as important as the legalistic ones. Parties take their time discussing deals. Managers meet to exchange meishi—their all-important business cards (usually presented with two hands)—and bow respectfully. It helps to establish confidence.

So it was that when a handful of bankers from Lehman Brothers met executives of Marubeni, one of Japan's largest trading houses, at Marubeni's headquarters across from the Imperial Palace last autumn, they never suspected that they were actually being drawn into a massive fraud. The teams had met numerous times to discuss a bridge loan. Reams of paperwork were supplied. In a convoluted agreement, Lehman provided more than $350m in financing to a small firm with ties to Marubeni (and founded by a cousin of the empress of Japan); the trading house guaranteed repayment.

Or did it? When Lehman contacted Marubeni after a payment was missed, Marubeni said that it had no idea what the bank was talking about. Marubeni has claimed that contracts signed and stamped by a Marubeni director were found to be forgeries and the manager whom Lehman's bankers met in Marubeni's offices was an impostor. Marubeni says the two employees who negotiated the deal were fired. Marubeni refuses to repay the money, claiming it is a victim of fraud itself. On March 31st Lehman sued Marubeni for $350m. Since the fraud was uncovered, more alleged victims have surfaced, such as Och-Ziff, an American private-equity firm, which is owed around $80m.

The case pits a company's responsibility to supervise itself against the adequacy of the due diligence that investors must perform. The Japanese legal doctrine of “apparent authority” holds firms accountable for their employees' actions, provided those actions are carried out within the scope of their normal work. Meanwhile, Lehman's checks will come under scrutiny, not least by its own insurance company. Yet also on trial will be Japan's business culture—and what constitutes trust in the world of finance.

In the West, that culture is increasingly one of implicit mistrust. Deals require armies of lawyers and thick paper trails to give parties confidence, in spite of the time and money that such work entails. In Japan, by contrast, companies—some dating back centuries—regularly deal with long-standing partners; reputational concerns, rather than strictly legal ones, are paramount. Business disputes rarely go to trial. The number of corporate lawyers is extremely low compared with other financial centres, and frauds by one party against another are exceedingly rare.

So when Lehman met Marubeni employees at the trading house's offices, there was no reason to suspect anything was amiss. Many consider such a culture to be very beneficial to Japan. Yet the closer that Japan's financial practices are to global standards, the more the informal ties of trust will be replaced with formal legal ones. Something will be gained, but something will be lost as well.