Bava Batra 94 - Acceptable Percentage of Inferior Merchandise
If one sells grain to his fellow, the buyer accepts upon himself one quarter of a kav in a se'ah measure, which translates into 1/24; for figs he accepts ten wormy ones per one hundred; for a cellar of wine he accepts ten barrels of souring wine per hundred. All these are general guidelines in the absence of a prevailing local custom, however, if there is an accepted custom, then it is binding.
If the buyer suspects that the grain contains more impurities than 1/24 and begins to sift it, and it is found that it contains more than the allowed 1/24, he may sift all the grain and return now ALL the impurities to the seller. Really one expects to receive good quality grain, only that he would not bother to sift. Once he started sifting, however, he can continue to sift all.
Art: Giovanna Garzoni - A Plate of Figs