A price for produce may not be fixed until the market price is known. When the market price is known, a price may be fixed, and although this one does not have, someone else does have.  [If] he was the first of the reapers, he may fix a price with him on the stack of grain, or on the vat of grapes, or on the vat of olives, or on the clay balls of a potter, or on lime after it has been sunk into the kiln. He may fix a price on manure all the days of the year. R’ Yose says: A price may not be fixed on manure unless he had manure in the dung heap; the Sages, however, permit [it].  He may fix a price with him at the best rate. R’ Yehudah says: Although he did not stipulate with him at the best rate, he may say: `Give me at such [a price], or give me my money.”