Kiddushin 60 - Betrothal with Delayed Payment
If a man said to a woman: "Become betrothed to me after thirty days," and someone betroths her in the interim, then when the thirtieth day arrives, the second betrothal remains effective and thus prevents the first one from going into effect.
If one says to a woman, "You are betrothed to me on the condition that I will give you two hundred silver coins (about $10,000)" - she is betrothed to him, and he owes her the money. When he pays, she it betrothed to him retroactively from the day of betrothal. Therefore, if she accepted betrothal from someone else in the interim, it is void. Others say that she is betrothed from the moment he gives the money, but not before. According to this, if someone preempts him and betroths her, he would loose her.
If he says to her, "Become betrothed to me, on the condition that I will show you two hundred coins," it is assumed that he should show his own money. If he shows her the money on the money changer's table, this is not good enough. However, this is obvious!? - The teacher includes even the case when the money he showed is part of a venture in which he has a share. Even that does not satisfy the condition.
Art: The Moneylender And His Wife by Quinten Metsys (detail)