How? [If] he took produce from him, but did not give him money, he cannot retract. [If] he gave him money, but did not take the produce from him, he can retract. They said, however: He Who exacted retribution from the people of the generation of the Flood and from the generation of the Dispersion will exact retribution from one who does not abide by his spoken word.  R’ Shimon says: Whoever has the money in his possession has the upper hand.