Baba Metzia 5:7-8

Baba Metzia 5:7

An agreement for produce (to be delivered at a later date) may not be reached until the market price is determined. Once that has been done, such agreements may be made because even if one supplier doesn’t have produce, another one does (so it could still be obtained). If the seller is the first to reap his crop (so the market price has not yet been set), the buyer may stipulate any price for the stack of grain, the basket of grapes or the vat of olives (i.e., for produce that the seller has on hand even if it is yet to be processed). The same is true of a potter's lumps of clay or of limestones in a kiln (which are also works in progress based on materials in hand). One may stipulate a price for manure at any point in the year. Rabbi Yosi says that one may not set a price for manure unless the seller has manure “in stock” on the dung heap but the Sages allow it. An agreement for produce may be made to lower the price if the market price drops. Rabbi Yehuda says that even if one did not make such a condition, the buyer can request the new, lower rate or he can void the transaction (since he has not yet taken possession of the merchandise).

Baba Metzia 5:8

A person may lend his sharecroppers a volume of wheat to be repaid with the same volume of wheat for use as seed but not as food (because the price may increase, raising the value of that measure of wheat). Rabban Gamliel used to lend wheat for use as seed in exchange for repayment in wheat. Regardless of whether wheat was expensive and went down in price, or whether it was cheap and went up in price, he would accept repayment based upon the cheaper price. This is not the law; Rabban Gamliel merely chose to act stringently in this matter.