Gemara

43a (Beraisa): If b'Shogeg Reuven gave Hekdesh money to a barber, he does not transgress Me'ilah until he makes Meshichah.

Another Beraisa says that he is Mo'el before Meshichah! One Beraisa discusses a Nochri barber, and the other discusses a Yisrael barber.

44a (Mishnah): If one paid for Levi's Peros but did not do Meshichah, Levi can retract. However, Chachamim said 'He who punished the generations of the flood and the dispersion, He will punish one who does not fulfill his word.'

R. Shimon says, whoever is holding the money has the upper hand.

47b (R. Yochanan): Mid'Oraisa, money acquires Metaltelim. Chachamim enacted that (only) Meshichah acquires, lest one sell something in his house, and a fire will erupt through Ones, and he will not strive to save it. If the item belongs to the seller (until Meshichah), he will strive to save it.

(Rav Chisda): Just like it was enacted that sellers can retract until Meshichah was done, also regarding buyers.

According to R. Yochanan, Chachamim hold like Rav Chisda, and R. Shimon does not.

48a (Beraisa - R. Shimon): Chachamim said 'He who punished the generations of the flood and the dispersion, the people of Sodom and Amora and the Miztriyim at the sea, He will punish one who does not honor his word.

48b (Abaye): Beis Din informs him that Hash-m will punish him.

(Rava): Beis Din curses him.

Abaye holds that it is forbidden to curse him - "v'Nasi v'Amecha Lo Sa'or"! Rava says that that applies only to "Amecha", one who acts like a Yisrael.

Rava learned from an episode in which people paid R. Chiya bar Yosef money to buy salt. Salt rose in price. R. Yochanan told him 'honor the sale. If not, you will accept on yourself 'He who punished...' If Beis Din merely informs him, there would be no need to inform R. Chiya bar Yosef!!

Objection: R. Chiya would not accept a curse of Chachamim! Rather, they gave partial payment. R. Chiya thought that he is obligated to sell only as much as was paid. R. Yochanan told him that he must honor the entire sale.

49a: A case occurred in which Reuven gave Shimon money for sesame, and the price went up. Shimon retracted and said 'I don't have sesame. Take your money back.' Reuven did not take his money; it was stolen.

Rava: Once he told you to take your money, he is not a Shomer Sachar. He is not even a Shomer Chinam! If Shimon will not give the sesame, he must accept Mi she'Pora!

Rav Tavos: That story was not like reported! Rather, Reuven came to me just before Shabbos, and asked to buy sesame. I refused. He asked to deposit his money with me. I said 'put it in my house where you want.' He did, and it was stolen. Rava ruled that I was not even a Shomer Chinam!

(Rav): Partial payment obligates the seller to give only the value of what was paid;

(R. Yochanan): It obligates him to sell the entire object.

Question (against Rav - Beraisa - R. Shimon ben Gamliel): R. Yosi and R. Yehudah argue about one who gave a security (to guarantee that he will buy a certain matter. However, if one was buying land and paid half the price, he acquires it all immediately. The rest of the money can be given years later.

Suggestion: The same applies to Metaltelim. Part of the money also 'acquires' all of them (regarding Mi she'Pora) without any Tenai.

Answer: No. Money truly acquires land, therefore, part of the money acquires all of it. Money 'acquires' Metaltelim only to obligate the seller to suffer a curse if he retracts. Part of the money does not 'acquire' all the Metaltelim.

Rishonim

Rif: The Halachah follows Rava, that Beis Din gives the curse. We learn that one who retracts is not considered one who acts like your nation. We cannot learn from the retraction from the sale of sesame, for it never happened.

Rif and Rosh (4:13): Rav Hai Ga'on says that since the seller could use the money for anything, it is like a loan. Even if he told the buyer 'take back your money' and the buyer did not come, the seller is responsible. The buyer need not take back his money until the seller accepts Mi she'Pora for retracting. A case occurred in which one paid money for wine, then feared lest a Nochri take it. Rav Chisda ruled that Meshichah was enacted also for buyers, so he can retract.

Rosh (13): Do not say that had the seller not said 'take your money', he would be a Shomer Sachar, for he has the right to use them. This is wrong. He may not use them until the sale is finished. Rav Huna holds like R. Yochanan, who says that money, not Meshichah, acquires mid'Oraisa. He must establish the Beraisa (that says that Me'ilah is only after Meshichah) to discuss a Nochri. We do not say that he is Mo'el once he gives money, for the barbar may use it! One could say that a Yisrael is different. Since he acquires mid'Oraisa through money, even though Chachamim enacted Meshichah, he may use the money once he received it. However, for us it does not matter. R. Tam said that since most of our business is through lending to Nochrim with Ribis, we are like moneychangers; surely we may use the money.

Rambam (Hilchos Mechirah 7:1): If one gave the money but did not do Meshichah, even though he did not acquire the Metaltelim, if the buyer or seller retracts, he acted unlike a Yisrael, and he must accept Mi she'Pora. Even if he gave a mere Eravon (partial payment), one who retracts accepts Mi she'Pora.

Rambam (Hilchos Mechirah (7:2): Beis Din curses him and says 'He who punished... He will punish one who does not fulfill his word.

Rosh (4:10): The Mishnah connotes that Beis Din need not inform or curse one who retracts; it just teaches that he will be punished. Even so, Abaye and Rava hold that Beis Din informs or curses him to strengthen the matter, for the masses are unaware of the punishment and are wont to retract before a Kinyan was made. Beis Din curses him connotes that the judge says 'He who punished... He will punish you if you will not fulfill your word.' However, the Rambam says that he says 'He will punish one who does not fulfill his word.'

Poskim

Shulchan Aruch (CM 204:1): If one gave the money but did not do Meshichah, even though he did not acquire the Metaltelim, if the buyer or seller retracts, he acted unlike a Yisrael, and he must accept Mi she'Pora.

Beis Yosef (DH u'Mah she'Chosav Bein): Since the curse is for not fulfilling his word, it applies to the buyer or seller.

R. Akiva Eiger: If the seller said that the buyer cannot retract, this is mere words and he can retract. However, if the buyer said that he will not be able to retract if the price drops, the Pnei Yehoshua leans to say that it takes effect. It is as if he said that if he retracts, he pardons the money. See Rema 198:5 (who says that if they stipulate that money will acquire, it acquires).

Shulchan Aruch (ibid): This is even if he gave only some of the money.

Beis Yosef (DH v'Afilu): R. Yochanan said that Eravon acquires totally, for Mi she'Pora for Metaltelim. We follow him against Rav

Shulchan Aruch (4): Beis Din curses him and says 'He who punished the generations of the flood and the dispersion, the people of Sodom and Amora and the Miztriyim at the sea... He will punish one who does not fulfill his word.

Shach (5): The Bach rules like this, unlike the Rosh.

SMA (8): The curse mentions those killed in the flood and the Mitzriyim, for Hash-m punished them through overt miracles and demonstrated His supervision over the world.

Rema: Some say that they say... He will punish you if you will not fulfill your word. Some say that they say this to him in public.

Beis Yosef (DH v'Chosav, citing Talmidei ha'Rashba): The words of the Gemara 'we curse him' connote that we curse him personally. However, the Rashba says that we merely curse Stam (one who does not fulfill his word). This is like the Mishnah, which taught Stam.

Shulchan Aruch (YD 175:7): If one gave money Stam (for Peros) and did not specify to receive at the cheap price, and the price dropped, he receives like the price at the time of the sale. One who retracts must accept Mi she'Pora.