Gemara

84b (Mishnah): If a buyer measured but did not do Meshichah, he did not acquire. If he is clever, he will rent the premises (to acquire immediately).

85a (Beraisa): In the seller's premises, he does not acquire until he does Hagbahah or takes it out of the premises. In the buyer's premises, he acquires as soon as the seller agrees to sell. In the premises of Levi (with whom the merchandise was deposited), he does not acquire until Levi agrees that the buyer may use the premises to acquire, or rents the premises to him.

Eruvin 79b (Mishnah): One can be Mezakeh (an Eruv) for others through his mature child, but not through his small child, for a small child's Yad (power of acquisition) is like his father's Yad (he acquires only for his father).

Kidushin 27a (Mishnah): R. Gamliel said 'a tithe (Ma'aser Oni) that I will measure off later is given to R. Akiva, to acquire it on behalf of the poor. I rent to him the area it rests on.'

Bava Metzia 116b (Mishnah): If Reuven owned a house and Shimon owned its upper story and it fell, they divide the wood, rocks and dirt.

Question: The one in whose Reshus the rocks are in, he is Muchzak. The other cannot take (whole rocks) from him without proof!

Answer: Partners freely lend their premises to each other.

Rishonim

Rif: In the premises of a Shomer, he does not acquire until Levi accepts, or until he rents the place.

Beis Yosef (CM 200 DH v'Da): The Rif's text does not say regarding a Shomer 'until he accepts', rather, 'until he does Hagbahah or removes it from his Reshus. (Note: our text of the Rif is like our Gemara.) The Ramban says that even according to this text, once he accepts, he acquires, for he removed it from the seller's Reshus. Even though the Ramban says that the seller said 'be Zocheh for Ploni', it seems that it suffices if he said 'give them to Ploni' and the Shomer consented. In any case we learn that the Shomer's consent helps when the seller tells him. It does not help if the buyer tells him 'Ploni sold them to me' and the Shomer consented.

Rebuttal (Shach CM 6): The Ramban says that if the Peros were in his hand and he said ''be Zocheh for Ploni', it works, for Zachin l'Adam. Also his Chatzer can be Zocheh for him. I say that he must say ''be Zocheh for Ploni.' If not, saying 'give' is not like saying ''be Zocheh for', since he does not hand over the Peros to him now, rather, they were deposited from before (CM 125:6).

Rambam (Hilchos Mechirah 4:6): If the seller measured the Peros into the buyer's Keli in the seller's Reshus or a Shomer's Reshus, the buyer does not acquire until he does Hagbahah or takes it out of the premises through renting the place or similar methods.

Magid Mishneh: Some texts say that in the seller's Reshus, he does not acquire 'until he accepts upon himself.' I.e. the Shomer's accepts to give them to the buyer with the seller's consent. Surely this suffices.

Rebuttal (Kesef Mishneh): I say that it suffices only according to those who had this text, but not according to the Rambam!

Rosh (Bava Basra 5:15): When the buyer puts his Kli in another's Reshus, it suffices for the owner of the Reshus to say that he lends the place to him. A buyer's Kelim acquires wherever he is allowed to put them. R. Gamliel needed to rent the place of the Peros to the Chachamim because they were not in the Kelim of the recipients.

Rosh (16): When one says 'my Kli or Chatzer should acquire for Ploni', this works. His Chatzer is like his Yad. He need not be Mezakeh through someone else. The Beraisa says 'in the Shomer's Reshus, he does not acquire until he accepts on himself or rents the Reshus.' This shows that acceptance works. If it worked in the seller's Reshus, the Beraisa would have taught them together (that acceptance works for either)! The seller can transfer his Chatzer to the buyer only through rental or a Kinyan, like we find with R. Gamliel and in Eruvin (one can be Mezakeh through his mature child, but not through his small child). This is because one cannot be Mezakeh his Reshus to another by himself.

Rashbam (85a DH ha'Mufkadim): We discuss when the seller deposited with a Shomer (Levi). Presumably, Levi was Makneh his premises to the seller for his Peros, to sell and measure them, like every Nifkad does.

Maharit (1:65): A case occurred in which a sick woman gave all her property, which was in her father's house, to her father. I say that it is as if a Kinyan was done, since one's property acquires for him. Someone derived from the Rashbam that a Nifkad is Makneh his premises to the seller, until he is Makneh it to the buyer to acquire. Therefore, the buyer must make a proper Kinyan on the premises in order to acquire. (We do not say that a buyer is Makneh his Reshus to the seller, who brought the Peros there haphazardly.) I say that the Rashbam does not discuss a proper Kinyan. It suffices to permit the buyer to put his Kelim there in order to acquire.

Ketzos ha'Choshen (189:1): The Tur says that if Levi deposited an item with David and agreed to sell it to him, he does not acquire. Why doesn't his Reshus acquire for him> The Taz says in the name of the Rashbam that a Shomer's Reshus is like the seller's Reshus, therefore, it does not work. The Maharit says that Levi acquires the Reshus only through Kesef or Chazakah. I answer that leaving one's wares in a Reshus is like eating Peros, and the Rambam (Hilchos Mechirah 1:15) says that eating the Peros acquires. Some disagree, but only about permanent acquisition. All agree that usage acquires the right to use it for the prupose he borrowed it.

The Maharit asked that Levi acquires only when the Shomer designates a place for the Peros. I say that the Shomer lent his land for wherever the Peros will be. Bava Metzia 116a proves this. When a house fell, even if the rocks are in the Reshus of one of them, he is not Muchzak, for partners freely lend their premises to each other. Rashi and the Nimukei Yosef explain that he is Mafkir his Reshus for his partner to put things, so it is as if they are in their joint Reshus. This shows that no Kinyan is required.

Poskim

Shulchan Aruch (CM 200:2): If Metaltelim were in the Reshus of the seller or a Shomer, the buyer acquires only after Hagbahah or Meshichah.

Gra (8): This is like the Rambam, who had the Rif's text.

Rema: If the buyer rented the place where the Peros are, or it was given to him for a gift with a Kinyan, or even through mere speech, he acquires, for now the Peros are in his Reshus. Words help when they are in a Shomer's Reshus. If they are in the seller's Reshus and he said 'my Chatzer should acquire them for the buyer' he does not acquire until he rents the place to him or the buyer acquires the place through a Kinyan. When the Peros are with a Shomer, saying 'my Chatzer should acquire for the buyer' helps only if the seller consents.

Beis Yosef (DH v'Im): The Rashbam says that the buyer acquires only after the Shomer agrees, on the seller's command, to designate his Reshus to the buyer to acquire, or the buyer rents the place. Acceptance (that he acquire) and rental help also when the Peros are in the seller's Reshus. The Beraisa discusses a typical case (the seller wants to clear the Peros from his property), so it teaches about Hagbahah and Meshichah. A Shomer is willing to guard Peros of the buyer just like he guarded for the seller, so, it teaches about acceptance and rental (the Peros remain there).

Rebuttal (Beis Yosef citing Tosfos): If both methods work whether the Peros are in the Reshus of the seller or Shomer, both should have been taught together! Also, it is unreasonable that acceptance help in the seller's Reshus, for one cannot be Makneh his Reshus to others by himself, like it says in Eruvin. One can be Mezakeh for others through his mature child, but not through his small child, for the latter's Yad is like his Yad.

Beis Yosef (ibid.): The Rosh, R. Yerucham and the Ramban hold like Tosfos.

SMA (5): The seller himself cannot be 'be Zocheh for the buyer by himself. A Shomer can say 'my Chatzer is Zocheh for what Ploni buys from Almoni', for his Chatzer is like his Yad, so it can 'be Zocheh for another just like his Yad could.

Gra (10): Kinyan does not help for rental. Money is required (Tosfos Bava Metzia and Kidushin (11a and 27a DH u'Mkomo), CM 195:9).