Q: Can the buyer or seller renege on an agreed price before delivery?
A: There are three stages in buying, each of which has a different halacha.
1. If there was only a verbal or informal written agreement, a person has a moral obligation to uphold his word, but it does not carry legal consequence. If is person recants his agreement, he is called mechusar amana, lacking trustworthiness. (Choshen Mishpat 204:7,11)
2. If the buyer paid for the purchase, but did not yet do an act of acquisition (kinyan), the parties have legal ability to recant, but are subject to a curse of Beit Din, mi shepara: "The One who punished the generation of the Flood and the generation of Dispersion will punish one who does not uphold his word." (204:1,4)
3. If the buyer already made an act of acquisition (kinyan), even if he did not pay yet, the transaction is legally completed and the parties cannot renege any more. (189:1) IY"H, we will discuss some common acts of kinyan in a later issue.