The weakness that forgers exploit is the method of connoisseurship, by which experts determine the attribution of a given artwork. The capacity for an Art Market to generate super-prices, so that materially similar objects can be sold for vastly different prices, simply based on a knowledge of who made them, often leads forgers to try to take advantage of that discrepancy. Forgery has been a recurring problem since art's origins, but in the last 10 years the New York Art World seems to have been shaken by one forgery scandal after another. With provenance itself becoming a target of forgeries, more institutions are investing in professionals whose sole activity is to study and validate documents and sources related to the provence of their collection. When Michael Knoedler arrived in New York in 1852 as a representative of the French lithographer Goupil & Cie, the city had virtually no art dealers to speak of.