65:17 If grain has a fixed market price, one may offer it for sale at advance payment at that price even if the seller does not yet have any such grain in stock. This is permitted because even if the price of the grain goes up, the buyer does not profit from having paid in advance since he could have bought the grain from another vendor at the time at the same set market price. Since the agreement was made in this fashion, which is permitted even if the price of the grain goes up before delivery, if the seller does not want to provide it at the agreed-upon price, he can deliver another type of produce or pay the financial equivalent of the current market value.
65:18 Let’s say that a person has merchandise for sale that is inexpensive in his location and more costly elsewhere and his friend asks to sell this merchandise in the more expensive place. The friend stipulates that he will have use of the money for a period of time, after which he will pay the person what he earned less his expenses. If the friend takes responsibility for the merchandise during the journey, such a transaction is prohibited; if the owner of the merchandise retains responsibility, it is permitted so long as the friend is paid a fee for his efforts.