Kiddushin, Chapter Two, Mishnah Two
A man may not deceptively betroth a woman; she must agree to her betrothal with full understanding of what he is giving her and under what conditions. This mishnah deals with a man who somewhat deceptively attempts to betroth a woman.
1) [If a man says to a woman], Be betrothed to me with this cup of wine, and it is found to be of honey, or of honey and it is found to be of wine;
2) with this silver denar, and it is found to be of gold, or of gold and it is found to be of silver;
3) on condition that I am wealthy, and he is found to be poor, or poor and he is found to be rich, she is not betrothed.
4) Rabbi Shimon says: if he deceives her to [her] advantage, she is betrothed.
In each case in this mishnah, the husband makes an incorrect statement as part of the betrothal formula. For instance, he states that he is betrothing her with a cup of a certain liquid and it turns out to be a different liquid. Alternatively, he says that he is betrothing her with a certain type of coin and it turns out to be a different coin. Finally, he tells her that he is of a certain economic status and he is not. According to the first opinion, since the facts as he stated them are incorrect, the betrothal is ineffective. This is true even if he deceived her to her own advantage. For instance, he said that he was giving her a cup of wine and it turned out to be a cup of honey, which is more valuable than wine. According to the first opinion, we dont reason that a woman who would agree to be betrothed to a certain man with a cup of wine would also agree to such a betrothal if done with a cup of honey, since she could always sell the honey to buy wine. Rather, the betrothal statement must be accurate.
Rabbi Shimon disagrees. He holds that if the deception is clearly to her advantage, the betrothal is valid. Therefore, if he says that the cup was honey and it turned out to be wine (cheaper) she is not betrothed. But if he told her that the cup was wine and it turned out to be honey, she is betrothed.