One comes to buy a field and says that he is buying it for the Exilarch (who was given a semi-royal authority over the Jews in Babylon.) He is really buying the land for himself, but he wants the deed to be written in the name of the Exilarch. He is doing it to discourage protesters to the sale, who might claim that they are the true owners of the land and not the seller.
The ruling then says we do not force the seller to write another bill of sale with the buyer's name. The seller might not want to write two bills of sale because it may look like he is selling the field twice. However, if the buyer stipulated that he would want two bills of sale, the seller has to produce them. But that is obvious? The seller can say that he thought the buyer was talking to the witnesses.
Art: The Ploughed Field by Van Gogh