A non-Jew asked Reuben to obtain a silver vessel for him. Reuben bought one from Simeon after explaining that the customer was his friend and that he didn’t want to deceive him. Simeon assured Reuben that the vessel was silver mixed with only a little copper.

Reuben paid Simeon 47 denarii and resold the vessel to the non-Jew for 50 denarii. The customer later discovered that it was actually made of copper, compelled Reuben to return his 50 denarii and gave him the vessel back.

Reuben then demanded that Simeon cancel their sale and return the 47 denarii. The rabbinic ruling held that Reuben was entitled to do so because this was a mistaken purchase rather than a simple disagreement over the object’s value. Simeon had represented a copper vessel as silver, and Reuben had relied on that representation.

Responsum 842, Teshuvot Maharam