Based on a Naaleh.com shiur by Dayan Shlomo Cohen
Every transaction has several stages. The first is the final decision to buy, the second is when the buyer and seller come to a verbal agreement, and the third stage is paying for the item. The overriding rule in what causes a transfer of ownership is gemirat daat-a final decision that the buyer and seller will now proceed with the transaction.
Asking and comparing prices does not create an obligation to buy. However, once the buyer makes a positive decision to purchase the item, our Sages say those who fear Hashem should stay true to their thoughts. Beit din will not take a stand if the buyer retracts at this point. However the next stage, when a verbal agreement is formed, creates an obligation. The Sages term buyers or sellers who retract at this level “mechusrai emunah“-unfaithful people. Beit din cannot force the buyer or the seller to keep his agreement, but the one who retracts is called a rasha and beit din will attempt to make him keep his word. If there is a fear of loss involved, then either of the parties may renege on the agreement.
There is an argument in the Shulchan Aruch and other Poskim whether a change in a situation allows a buyer or seller to go back on his word. The Shulchan Aruch rules that it makes no difference and each party must stand by his word. The Rema agrees with this. If either the buyer or seller dies, according to some opinions, his heirs should keep the agreement.
According to the Chasam Sofer, a change in a situation may allow a person to go back on an agreement but it does not apply to every change. Indeed Rav Wosner rules that one may nullify an agreement due to a significant change but not because of a small change. Overcharging 1/6th more than the market value, nullifies a sale. If it is less than 1/6 it is valid. If it is exactly 1/6, one must return the 1/6th and the agreement remains valid. The same holds true for the seller. If he finds out that he can now sell an item for 1/6th more he may go back on the agreement. If it is less than 1/6 he cannot.
Once an agreement is reached and it is written down and signed, there is an obligation to supply the goods and pay. A signature is considered a kinyan and obligates both the buyer and the seller. It is considered more severe than mechsurei emunah.
What happens if you make a verbal agreement with two people simultaneously? The stigma of mechsurei emunah can be removed by appeasing one side verbally or monetarily. You can sell to the second and appease the first or visa versa.
Giving a gift also depends on gemirat daat. Telling someone you will give a gift doesn’t create a transfer of ownership. A small gift creates an obligation. Offering a large gift doesn’t create an obligation because the listener does not believe you anyway. A rich uncle who promises his nephew a bike must stand by his word. On the other hand if he promises him a car, there is no obligation. A poor uncle who promises a bike is not obligated. However if he promises him a small gift such as a book, he must keep his word.
A decision to give to charity involves no change of ownership. However according to some Poskim, a final thought creates an obligation akin to a vow and beit din can force someone to keep it. Other Poskim disagree and maintain that thoughts do not create a vow. All opinions hold that a verbal donation is a vow. Generally children cannot be forced to keep their parent’s vows to charity but it is fitting that they should. If after a vow was made, the situation changes, the obligation can be nullified. If you pledge tzedakah on the condition that someone will survive, and he does not, there is no obligation to honor the pledge. If you say, “In order that he should live,” one must follow through with the donation. The same way a debtor must pay his debts, one must keep one’s charity obligations even when it becomes financially difficult.
The Shulchan Aruch rules that one should not take charity from a married woman because she may not have her husband’s permission. Poskim today rule differently since times have changed and woman are more in charge of the home.
In the diamond exchange, a verbal agreement usually finalizes a transaction and the buyer and seller wish each other mazel u’bracha. In Jewish law, this is considered a final agreement and a transfer of ownership.