Gemara

85b - Question (Rav Sheshes): Does a buyer acquire with his Kelim in the seller's premises?

Answer #1 (Rav Nachman - Beraisa): In the seller's premises, he does not acquire until he does Hagbahah or takes it out of the premises.

Suggestion: This is even if the Keli belongs to the buyer.

Rejection: No, it is only when the seller owns it.

Question (Seifa): In the buyer's premises, he acquires as soon as the seller agrees to sell.

Answer: The Seifa discusses the buyer's Keli.

Answer #2 (Rava - Beraisa): If Peros were unloaded and brought them into the buyer's house, if they set the price, even if they did not measure, neither party can retract.

Inference: Just like the seller's Kelim do not acquire in the buyer's premises, also the buyer's Kelim do not acquire in the seller's premises!

Rejection (Mar bar Rav Ashi): The merchandise was bundles of garlic, which are not put into Kelim.

Bava Metzia 9b - Question (R. Elazar): If Reuven said 'Meshoch (take to your Reshus) this animal and acquire the Kelim on it', does Meshichah on the animal acquire the Kelim? (The Gemara never answers the question.)

Rishonim

Rif: A Beraisa teaches that if Peros were unloaded and brought them into the buyer's house, if they set the price, even if they did not measure, neither party can retract. Mar bar Rav Ashi established this to discuss bundles of garlic, which are not put into Kelim. Hasd they been put in the seller's Kelim, the buyer would not acquire.

Rashbam (86a DH Pirkan): The Gemara inferred that the seller's Kelim do not acquire in the buyer's premises, for the Peros are still in the seller's Kelim, yet they do not prevent the buyer from acquiring through his premises).

Tosfos (86a DH umid'Kelav): The Gemara knew that the buyer acquires through his Reshus, and not through Meshichah, for it connotes that he acquires even if the seller unloaded them.

Rosh (5:15): Saying 'go acquire' does not help for the seller's Kelim in the buyer's Reshus, for this does not connote that he lends the Keli to him in order that it would be considered the buyer's Keli.

Beis Yosef (DH v'Heilach): Later, the Rif brings Rav's law that what was measured out acquires, i.e. in a Simta, or in the seller's Kelim in the buyer's Reshus. This contradicts what he said that the buyer's Kelim do not acquire in the seller's Reshus unless the seller said 'go acquire'! Perhaps measuring helps like 'go acquire.' Or, saying 'I sell a Se'ah for a Sela' is like saying 'go acquire', and this helps also for the seller's Kelim in the buyer's Reshus, unlike R. Yonah. The Rosh says that the Rif holds that the seller's Kelim acquire in the buyer's Reshus. Surely, his text of the Rif omitted Mar bar Rav Ashi, who says otherwise. The Rif did not learn from here that the buyer's Kelim acquire in the seller's Reshus (for it is not Batel to the Reshus). Since Mar bar Rav Ashi rejected the proof from unloading the Peros, it is possible to say that neither acquires. Also the Rambam says so.

Rambam (Hilchos Mechirah 4:1): One's Kelim do not acquire in Reshus ha'Rabim or in the seller's Reshus, unless the seller said 'go acquire in this Keli.'

Rambam (2): Just like the buyer's Kelim do not acquire in the seller's Reshus, the seller's Kelim do not acquire for the buyer, even in the buyer's Reshus.

Magid Mishneh: The Gemara explicitly said that the seller's Kelim do not acquire in the buyer's Reshus. However, this was according to the opinion that the buyer's Kelim acquire in the seller's Reshus! Perhaps since this is how we establish the Beraisa, it is according to all opinions. The Ri mi'Gash says that since the buyer seeks to take from the seller, he must bring a proof whether it depends on the Keli or the Reshus (and since the Gemara never resolved the question, he cannot), so he does not acquire.

Beis Yosef (DH v'Hinei): The Ri mi'Gash holds like the Rosh, that it is a Safek whether it depends on the Keli or the Reshus. It seems that the Rambam disagrees! He said 'he does not acquire.' When there is a Safek, the Rambam writes 'it is a Safek'! Likewise, the Rif wrote 'he does not acquire.' He did not write 'the question was not settled'! Rather, in the text of the Rif and Rambam, both questions were asked. Rav Huna answered that the buyer's Kelim do not acquire in the seller's Reshus, and we hold like Mar bar Rav Ashi, that the seller's Kelim do not acquire in the buyer's Reshus. Also Mar bar Rav Ashi holds like Rav Huna! He did not come to reject the proof, rather, to teach how we establish the Beraisa. The Rif needed to explain like this, for he holds that the Halachah follows Rav Huna, even though Mar bar Rav Ashi is Basra. How did the Rif and Rambam know that Mar bar Rav Ashi really holds like this? Perhaps he merely dispels the proof! He gave a difficult answer (we discuss bundles of garlic, which are not put in Kelim). He would not do so unless he was forced, i.e. for he holds that this is true.

Rosh (ibid.): We tried to answer the question from a Beraisa which says that one does not acquire until he does Hagbahah or takes it out of the premises. We rejected this, for perhaps this refers to the seller's Keli. We learn from here that Meshichah helps in the seller's Keli. Also, in Bava Metzia we asked whether Meshichah of an animal acquires the Kelim on it. This implies that we ask only about an animal, for it does not become a basis for the Kelim, but surely Meshichah of Kelim acquires the Kelim (it seems that the last word should be 'Peros') inside them, even if he did not say 'be Moshech the Keli to acquire the Peros,' rather, the buyer did Meshichah in front of the seller. In the conclusion, it is possible that the buyer's Keli acquires even if the seller's Reshus. The Beraisa teaches them separately, for in the buyer's Reshus he acquires without measuring. Putting in his Kelim is like Meshichah. The seller's Reshus is no better than a Simta, and he must measure to acquire. Our question was not settled. We do not know whether the Keli is Batel to the Reshus, or vice-versa. Therefore, the buyer's Kelim in the seller's Reshus or vice-versa does not acquire.

Poskim

Shulchan Aruch (CM 200:5): Just like the buyer's Kelim do not acquire in the seller's Reshus, the seller's Kelim do not acquire for the buyer, even in the buyer's Reshus.

Beis Yosef (DH v'Chosav): The Ramah says that since we do not know which of these two ways acquires, if a buyer bought two things from a seller, one in each way, the seller must give one of them to him. He may choose which. We learn from one who told his son 'one of my documents (against borrowers) was already paid.' If the father has two documents against one borrower, the larger loan is paid. If two buyers bought from one seller, each in a different of these two ways, they may take one from the seller if one writes a Harsha'ah (power of attorney) to the other.

Rema: Some say that even if the seller said 'go acquire', he does not acquire.

Beis Yosef (DH u'Piresh): Why did the Tur cite this in the name of R. Yonah, and not in the name of the Rosh? It seems to me that the Rambam disagrees.

Beis Yosef (11 DH v'Im): The Rambam rules that the seller's Kelim do not acquire in the buyer's Reshus, but regarding a sale of 'a Kor for 30 Sela', he holds that measuring into the seller's Keli helps! We must say that measuring is like saying 'go acquire.' The Rambam holds that 'go acquire' helps for the seller's Kelim in the buyer's Reshus, unlike the Ri mi'Gash.