Gemara

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 even a Shomer Chinam.

Rav Tavos: This is what really happened. Reuven asked to buy my sesame; I refused. He asked to deposit his money with me before Shabbos. I said 'put it anywhere in my house.' Rava ruled that I was not a Shomer at all!

Bava Kama 118a (Mishnah): If Reuven received a deposit or borrowed from Shimon in a Yishuv (settled area), he may not return to him in the Midbar (wilderness).

Contradiction (Beraisa): A loan may be paid anywhere. An Aveidah or deposit may be returned only to its place.

Answer (Abaye): The Beraisa means that one may demand payment of a loan anywhere. One may demand an Aveidah or deposit only in its place.

Rishonim

Rif (29b): 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 the curse 'Mi she'Pora' for retracting.

Rif (Bava Kama 44a): We learn from the Mishnah and Beraisa that one who lent in a Yishuv may demand payment in the Midbar, against the borrower's will. However, the borrower cannot pay up in the Midbar against the lender's will. The money is in the borrower's Achrayus (he suffers any loss to it) until they return to the Yishuv. This refers only to a loan.

Rambam (Hilchos Malveh 13:8): One may demand payment of a loan anywhere. If one lent in a Yishuv and demanded payment in the Midbar, the borrower cannot resist. He must pay him whenever he claims. If the borrower wants to pay in the Midbar, the lender may opt to receive, or to say 'I will be paid only in a Yishuv, just like I lent to you in a Yishuv.' The money is in the borrower's Reshus until he pays in a Yishuv.

Rosh (Gitin 7:7): Obviously, a borrower can repay Bal Korcho of the lender. Only in the Midbar he cannot force him to accept payment.

Tosfos (Gitin 75a DH Michlal): We learn this also from Bava Metzia 49a. Hillel needed to enact that payment Bal Korcho works for Bayis Ir Chomah, for there the buyer loses through it.

Poskim

Shulchan Aruch (CM 74:1): (One may demand payment of a loan anywhere,) even if David lent to Levi in a Yishuv, he can demand payment in the Midbar and force Levi to pay there, if Levi has enough to pay and return to the Yishuv. If David claims 'surely, he has enough for both', and Levi says 'I have enough only to return to the Yishuv', he swears Heses.

Source (Tur, citing the Ramban): Surely, if David lent to Levi in a Yishuv and found him in the Midbar, he cannot force him to pay there. Who will finance Levi there?! If Levi says that he has only enough money to return to the Yishuv, he need not pay. Even in a Yishuv, we are Mesader (leave a borrower with essentials) and allow him food appropriate for him. Rather, David said 'pay me here, for I know that you have enough to pay me and for your food', and Levi said 'I have enough only to return to the Yishuv.' He swears Heses that he does not have enough to pay the debt.

Drishah (1): The Ramban (cited in Sefer ha'Terumos 30:1:2) connotes that the difference in the Beraisa between a loan and deposit is that David cannot make Levi swear about a deposit, for presumably he did not bring it. This cannot be, for Shevu'as Heses was not enacted until the Amora'im! (This is difficult for the Tur; Sefer ha'Terumos did not say Shevu'as Heses.) Further, surely he cannot make him swear about a deposit if he is unsure if he has it! Rather, David says 'in my estimation, surely you have enough (or, my deposit).' This does not suffice for a deposit, for it is unlikely that Levi took it. The Tur does not literally mean Heses, rather, an oath less severe than other oaths of the Mishnah. The Ran (Shevuos 31a) says that a Shevu'ah like Heses applied in certain situations at the time of the Mishnah.

Gra (4): We learned that he cannot demand payment in the Midbar. This implies that he can demand payment in a Yishuv, even if it was not the place of the loan.

Shach (1): Shiltei ha'Giborim (Makos 1b:2) was unsure if Levi must bring the money if David claims it in a place that was not the place of the loan, and Levi has no money there. I say that surely, he need not.

Shach (3): Shiltei ha'Giborim was unsure if money owed for wages or a sale is like a loan, or like a deposit. Surely, it is like a loan. A deposit is different because the Shomer was supposed to leave it in its place!

Shulchan Aruch (ibid): If Levi wants to pay in the Midbar, David may refuse to accept until reaching the Yishuv, just like he lent in a Yishuv. However, Levi can force him to accept in any Yishuv, even if it is not the residence of David or Levi, or the place of the loan, and even if David must pass several Midbaros until reaching his place.

SMA (1): Even though Levi cannot force David to accept the money here, David has the upper hand because he gave benefit to Levi.

Shach (5): Shiltei ha'Giborim says that if Levi found David in a Yishuv outside of David's residence, and wants to pay with the local currency which is not accepted in David's home, if there was no stipulation, David must accept it.

Shach (293:1): Gidulei Terumah asks what is the Chidush of the Mishnah. I say that the Chidush is that even though the borrower cannot force the lender to accept payment, the lender can demand payment

Shulchan Aruch (ibid): A caravan is considered like a Yishuv.

Source: Tosefta 10:14, cited in Beis Yosef (3).

SMA (4): There is no danger of theft in a caravan.

Shulchan Aruch (CM 120:1): If Levi said 'take your money', and the lender refused, and he threw it to him in a proper place to pay, he is exempt, for one can pay a loan Bal Korcho. Similarly, if he said 'your money is in my house. Take it', and the lender refused, he is exempt if it was lost without negligence.

Beis Yosef (DH Kosav): The Mordechai (Gitin 394) and R. Yerucham say that one can pay a debt Bal Korcho of the lender.

Darchei Moshe (2): The Mordechai (Gitin 427,428) says that Riva and Avi ha'Ezri disagree. Even the lenient opinion exempts only when he has the money here, and the lender refuses to accept it. However, the Ramban exempts even if he said 'I will bring your money' and the lender left.

Beis Yosef (74 DH Motzasi): Maharam says that if the money was wrapped in the borrower's house, he is liable, for if a good deal arose, he would use the money. However, one is exempt for a deposit once he says 'take your item.' I obligate also for a deposit of coins, for he can use them.

Question (Darchei Moshe 2): Once he ceased to guard them, why should he be liable against his will?

Answer (Hagahos Drishah 2): If a grocer accepted a deposit of coins (and they were not wrapped in a special way), even if he did not use the he is a Shomer Sachar because he could use them (Bava Metzia 43a).

Gra (6, b'Sof): One is exempt for a deposit once he says that he is ready to return it. One is not exempt for a loan until he returns it. However, payment Bal Korcho is valid.

Gra (5): We follow Version #2 of Rava (Gitin 75a, who says that payment Bal Korcho is valid). Rav Papa was uncertain, so we rely on Rava, who was sure. The Rambam and Shulchan Aruch are stringent about a Get, but not about money. Tosfos proved that regarding a loan, all agree that payment Bal Korcho is payment.

Rivash (197, cited in R. Akiva Eiger): If Ploni came to pay for Levi, and he was not his Shali'ach, David need not accept from him.

Rema: Some disagree (Mordechai Gitin 394).