Thus, if the bracelet is stolen after Reuven gives the necklace to Shimon, Reuven cannot demand that Shimon return the necklace. Since the bracelet had already come under Reuven's ownership before the burglary, he incurs the loss, and not Shimon.
The Shulhan Aruch restricts this Halacha of "Kinyan Halipin" to an exchange of goods, to the exclusion of a cash transaction. For example, if Reuven agrees to sell his diamond necklace to Shimon in exchange for $10,000 that Shimon has in his safe deposit box, the cash does not come under Reuven's ownership once he hands the necklace to Shimon. Hence, if after he transfers the necklace the cash is stolen, Shimon must either return the necklace or pay $10,000. Since the stolen money had never come under Reuven's ownership, Shimon incurs the loss and must return or pay for the necklace.
Earlier in Hoshen Mishpat (201:1-2), the Shulhan Aruch addresses the Halachic status of handshakes as the consummation of transactions. He writes that where it is customary for dealers to formally close a transaction with a handshake, a handshake renders the agreement Halachically binding. For example, it was customary among diamond dealers to treat a handshake as creating a binding agreement, as if it were written in a contract. Where this has become the general practice, a handshake creates a Halachically binding agreement, as well.
However, the Halachic status of a handshake as the consummation of a transaction applies only to merchandise regarding which a handshake is commonly regarded as such. The fact that diamond dealers formally close deals with a handshake does not affect the status of a handshake in the context of automobile transactions, for example. Since car sales are not normally finalized with a handshake, shaking hands does not effectuate a change of ownership. Hence, if after the parties shake hands the car is stolen or damaged, the seller incurs the loss, rather than the buyer, since the car had still been under his possession.
(Taken from Dayan Shelomo Cohen's work "Pure Money," vol. 1, pp. 72-3)
Summary: When two parties agree to a barter exchange of goods, once one party transfers the given object to the other, he assumes legal possession over the other item, even if it still in the first owner's home. In societies where a handshake constitutes the consummation of a transaction, Halacha, too, treats it as such, and the sale is effectuated with the shaking of hands. This applies only to merchandise regarding which handshakes are looked upon as the formal consummation of a deal. With respect to other merchandise, however, such as cars, a handshake does not effectuate the sale and the car remains in the seller's possession even after the handshake.
