The Mishna on our daf deals with cases where a man offers to marry a woman, but he misleads her, either about the value of what he is offering her at the time of the marriage, or even about himself. Thus, in situations where a person says “marry me with this gold coin” and it turns out to be silver, or “marry me on the condition that I am a wealthy man” and it turns out that he is a poor man, the marriage will not take place. According to the Tanna Kamma this is true even if the misleading statement hides something of even greater value than was promised, e.g. if he assures her that he is poor, when he is really wealthy or he offers her silver and it turns out to be gold. Rabbi Shimon disagrees with that last ruling.
In explaining the reasoning behind the Tanna Kamma‘s ruling that even if what the prospective husband gave was better than what he promised the kiddushin will not work, the Gemara refers to a parallel case where a person offers to sell someone vinegar and it turns out to be wine. In such a case the sale is invalid because the purchaser may prefer vinegar to wine. Similarly in our case, perhaps the woman prefers silver to gold.
Tosafot Ri”d raises a question that disturb many of the commentaries – if someone is unhappy with gold and prefers silver, they can certainly arrange for an exchange. Why would that present an obstacle to the marriage? The simple answer is that we are not interested in the value and possibilities for exchange as much as we are interested in the immediate possibilities of use. According to many of the rishonim, silver is more easily used for purchase and exchange than is gold.
Rav Ya’akov Emden suggests a different concern, namely that gold is more often counterfeited than is silver, and that is the woman’s concern.