Paul Quatrochi, a private dealer in Manhattan, only found out that the Art Loss Register (ALR) was now listing fakes when it asked him about a collection with which he was familiar. The ALR, which maintains a list of stolen works, wanted his opinion on whether certain pictures were fakes.

Quatrochi said that he regarded both the collector and his holdings with some scepticism. “He has two Vermeers. Two!” he chortled. An unusual claim that positively demanded scrutiny. “They are hard to date. I’d put them at about 1920.” But Quatrochi, who is trained in art law, noted that this was highly litigious territory and wondered if the ALR knew what it was getting into.