Gemara

(Rava): All Sechorah (business, e.g. buying and selling) is forbidden (on Chol ha'Mo'ed).

(R. Yosi bar Avin): If it is Devar ha'Eved, it is permitted.

Ravina had merchandise worth 6,000 (Dinarim). He waited until after the Mo'ed to sell it, and sold it for 12,000.

Ravina: People of a certain city owe money to me. May I go on Chol ha'Mo'ed to collect it?

Rav Ashi: Since you can find them now but will not be able to find them at another time, it is permitted, like Devar ha'Eved.

13a (Mishnah): We may not buy houses, slaves or animals unless needed for the Mo'ed.

Rishonim

The Rif and Rosh (1:23 and 2:18) bring all these teachings. Their text includes rocks among the things that may be bought only for the need of the Mo'ed.

Nimukei Yosef (DH Shahei): Ravina had an opportunity to sell his merchandise to one buyer on Chol ha'Mo'ed. It was Midas Chasidus not to, for he expected that this would force him to sell it bit by bit afterwards and lose greatly. He wanted to collect his debt on Chol ha'Mo'ed because this is when the borrowers are found at home.

Rif (Sof 6a): One may move merchandise that is about to get ruined. One may buy from a caravan during the Mo'ed.

Nimukei Yosef (DH Hada): Even though we do not permit exertion for profit, something that is not exertion, such as Sechorah, is considered Devar ha'Eved.

Rosh (1:23): Sechorah is forbidden because it is an exertion. Devar ha'Eved is only if one will lose from the principal, like olives that were turned over or a loan that will not be paid. If the market day is during the Mo'ed and afterwards he cannot profit as much but he will not lose from the principal, he may not sell during the Mo'ed. The Yerushalmi connotes that loss of a profit not normally found is Devar ha'Eved. One may do Sechorah with a caravan selling cheaply or buying for a high price if there will not be a similar opportunity afterwards.

Rosh (1:24): R. Tam says that the Isur of Sechorah on Chol ha'Mo'ed applies only to buying and selling, but not to loans.

Question: Ravina was permitted to collect his debt only because this was his only opportunity. Otherwise it is forbidden, and all the more so to lend!

Answer (Rosh): Ravina used to lend money and receive wine in return, so the loan was like a sale. The Mishnah (18b) supports R. Tam. It forbids writing a loan document. This implies that the loan itself is permitted. This is even if the loan is not needed for the Mo'ed, for the Seifa discusses loans needed for the Mo'ed.

Ri (brought in Rosh): I cannot forbid, since the custom is to be lenient like R. Tam. One who refrains will be blessed. I say that one who lends to Nochrim on interest should use for Simchas Yom Tov the interest paid for the first week.

Rosh (ibid.): In Ashkenaz, Yir'ei Shamayim do not lend to Nochrim on interest during the Mo'ed. In my house I permitted to lend to Nochrim who normally borrow from us, for if not they will get used to going elsewhere, and this is Devar ha'Eved.

Hagahos Ashri: The Rashbam was afraid to permit loans. It is not clear if one may collect from a Yisrael if he could collect after the Mo'ed. Rashi permits collecting debts from a Nochri if one does not have a security; the Rashbam blesses those who are stringent. The Ri said that when lending to Nochrim on interest during the Mo'ed, one should exempt them from interest for the week of the Mo'ed.

Beis Yosef (OC 539 DH u'Mah she'Chosav Rabeinu): Perhaps the Rashbam is stringent because not collecting now is not a Vadai loss.

Nimukei Yosef (4b DH uv'Devar): The Isur of Sechorah on Chol ha'Mo'ed is only a decree, lest one write. Some say that we did not decree if it prevents one from profiting, and therefore one may lend to Nochrim on interest. The Ramban argues. He permits buying from a caravan only things that one himself will need, but not buying to resell for profit, for loss of profit is not Devar ha'Eved. All agree that one may collect a debt or establish how much is owed, for this is Devar ha'Eved.

Rivash (Teshuvah 320, brought in Beis Yosef OC 539 DH v'Chosav ha'Rivash): Even the Ramban would permit selling if one can get a higher price during the Mo'ed. This is the biggest Devar ha'Eved there is, for right now his merchandise is worth what they are willing to pay for it. This is like R. Yosi bar Bun in the Yerushalmi. However, the SMaG allows selling only to avoid a loss of principal. He rules like R. Muna in the Yerushalmi, or he had a different text. One need not protest against those who are lenient about mid'Rabanan matters like this in which many are lenient. I suggest that it is better to be stringent.

Beis Yosef (ibid.): The Rambam and Rosh are lenient. It seems that the Rif and Ge'onim agree, for they simply cited the Yerushalmi (to permit buying from a caravan), implying that even in order to profit is permitted. One may rule to be lenient, unless there is a custom to be stringent.

Question: The Rosh says that loss of a profit not normally found is Devar ha'Eved. If so, why does he forbid to sell on the market day during the Mo'ed if afterwards he cannot profit as much?

Answer (Beis Yosef DH v'Ika and DH u'Mah): There will be a market day the following week, and he can make the same profit then. We are not lenient about a Safek Devar ha'Eved. A caravan is a sure Devar ha'Eved.

Beis Yosef (DH v'Chosav Mahari): Mahari Kolon says that if a periodic fair occurs on Chol ha'Mo'ed, this is like a profit that he already made. Even those who forbid Sechorah with a caravan would permit this.

Rambam (Hilchos Yom Tov 7:22): We do not do Sechorah during the Mo'ed, either buying or selling. If it is a Devar ha'Eved that is not always found after the Mo'ed, e.g. if ships or caravans arrived or they are about to leave, and they are selling cheaply or buying for a high price, one may buy or sell. We may not buy houses, slaves or animals unless needed for the Mo'ed.

Magid Mishnah: One may buy other things even not for the need of the Mo'ed. The Isur of Sechorah even on Yom Tov is only a decree. Therefore Chachamim did not forbid what one needs to use or resell for profit, except for houses, slaves or animals not needed for the Mo'ed, for such sales become known. Fields and vineyards are also forbidden; the Mishnah listed only things that are sometimes needed for the Mo'ed.

Rosh (8): If a Nochri pays a debt with wine, one may take it. This is like saving the debt (lest the Nochri refuse to pay later).

Poskim

Shulchan Aruch (OC 539:1): All Sechorah is forbidden, both buying and selling.

Rema: If one has an opportunity for a big profit during the Mo'ed he may sell covertly and spend more for Simchas Yom Tov than he originally planned.

Gra (DH Mihu): Many Poskim permit all Sechorah, because the Mishnah forbids only houses, slaves or animals, for such sales become known.

Magen Avraham (2): One may not plan to sell on Chol ha'Mo'ed if it was possible beforehand. We similarly forbid planning to remove flax from water during the Mo'ed, even though this is not a Melachah.

Shulchan Aruch (2): One may collect a debt from a Yisrael, and all the more so from a Nochri.

Mishnah Berurah (7,8): This is not considered Sechorah. One may even go to another city and have the case judged by judges.

Kaf ha'Chayim (19): The Levush permits only if there is no security. The Eliyahu Rabah permits even payment that is a sale when there is no security, and payment of money itself when there is a security.

Shulchan Aruch (4): One may sell merchandise only if he will lose from the principal if he does not sell it during the Mo'ed.

Shulchan Aruch (5): Something that is not always found after the Mo'ed, e.g. if ships or caravans arrived or they are about to leave, and they are selling cheaply or buying for a high price, one may buy or sell. This is even if he buys solely for profit. The same applies to periodic fairs (when one gets better prices than usual).

Magen Avraham (6): We permit profit if it is no exertion.

Mishnah Berurah (19): Perhaps we similarly permit to sell when the Nochri holiday follows Chol ha'Mo'ed, and they buy much more than usual.

Rema: One may even travel to another city for a fair.

Bi'ur Halachah (DH v'Afilu): Exertion is forbidden for the sake of profit (Siman 537). We must say that here we discuss one whose livelihood is from fairs. For him it is Devar ha'Eved.

Shulchan Aruch (ibid.): This does not apply to when there is a weekly market day, for one can wait to sell it on the market day after the Mo'ed.

Magen Avraham (5): It is forbidden only if he is sure that he will not lose from the principal.

Taz (3): One may sell if one door of the store is closed and he will use (some of) the revenue for Simchas Yom Tov.

Rema: A wholesaler is permitted, for it is Devar ha'Eved (for him).

Question (Magen Avraham 8): It is Devar ha'Eved because if he would buy now, he could resell for a profit on the next market day and buy a larger amount. The same applies to all sellers! It is difficult to say that we forbid only one who sells the produce from his land (he does not buy and resell)!

Answer #1 (Magen Avraham): Here we permit only if the store is closed, and when the buyer comes he opens it slightly.

Answer #2 (Kaf ha'Chayim 40): Regular (retail) sellers normally sell a bit at a time, so it is not Devar ha'Eved for them.

Shulchan Aruch (8): If a Nochri pays a debt with wine, one may take it. This is like saving the debt.

Gra (DH Eino Yehudi): This is forbidden regarding a Yisrael. Nowadays even if he has a document he may be paid by a Nochri.