求翻译：As agency, such as gallery, art auction, museum and broker, they always drive up the fame of artist through a lot of speculation or use other forms to stir up the art market order, aiming to raising the price of artwork and getting more profit. In the great contemporary art bubble, it mentioned that under the non-rational prosperity background, the kind of price transparency is missing in the art market, which is controlled by two auction houses: Sotheby and Christie. In the abnormal economic phenomena behind, the price of contemporary art increased 800% from 2003 till 2008, Sotheby auction offer price guarantee to seller and also more than 50% leverage to buyer.是什么意思？

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