Fixing the price of milk by testing it

Question

(1) In our area it is customary that people buy milk and fix its price in this way: there is a vial for testing milk, by which it is known whether the milk is bad or good. If there is no change, twenty kilos come to seventeen rupees; if the reading is number two and a half, sixteen rupees; and if it is number two, fifteen rupees. And they do not measure it daily, but measure it two or three times a month. Is this arrangement permissible or not? If it is not permissible, then why? (2)

Answer

(1, 2) At the time of concluding the contract of sale it is necessary that the price be known; when the price is unknown, the sale is not valid. In the case asked about, at the time of the contract the price is not known and fixed but uncertain; therefore this sale is not valid.

Source: Fatawa Mahmudiyya

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