All commerce is forbidden,¹ since it often involves physical or mental stress which detracts from the festival. (Magein Avraham 539:1, Mishnah Berurah) It is also prohibited because of the fear that you might write something that is not permitted to be written on Chol Hamoed. (see Yeshuos Ya’akov) whether buying or selling.² 539:1. However if you have an opportunity to make a big profit,³ you may buy and sell in private.⁴ 539:1. This restriction is only in a situation when you have sufficient money, or, according to the Taz, when you are extremely wealthy. But if you are not, then you may buy or sell, even openly and for a modest profit; provided you use some of this profit for enjoying the Yom Tov. You also should keep your store gate closed until a customer arrives. (see Mishnah Berurah 539:5, 6, 17, 18, Sha’ar Hatziyun 539:7, Biur Halachah 539:4, and Chayei Adam 112:2) You should then spend more in honor of Yom Tov than you had previously intended.⁵ See footnote 4. (Biur Halachah 539:5) You are not permitted to do a melachah (like cutting material to sell) even under these conditions.

footnotes: ¹ The Sages prohibited commerce on Chol Hamoed, ² Shulchan Aruch ³ In this case, even if the opportunity may be there afterwards, it is permitted, for if the opportunity will be lost, it would be permitted even without the conditions listed. See paragraph 3. ⁴ Ramah ⁵ Ramah.

If you have merchandise and you are afraid that if you don't sell it now, its value will become less than its cost, you are permitted to sell it, because you prevent a loss thereby. However, if there is no fear of sustaining a loss, except that you will not make a profit later, you are forbidden to sell it, because unearned profit is not considered a loss.⁶

footnotes: ⁶ See footnotes 4 and 5.

If a fair occurs on (Chol Hamoed), that is, a market day which occurs infrequently, or even the weekly market day, which occurs before the non-Jewish holidays,⁷ when many buyers come together, you are permitted to sell in that market. Since it is an irregular occasion, even a lack of profit is considered a loss. But to sell in a regular weekly market is forbidden. Merchants or ships that arrive occasionally, and sell merchandise cheaply, or buy at a high price, which is something that does not happen often, you are then also permitted to buy from them and sell to them.

footnotes: ⁷ Before the non-Jewish holidays there is usually heavy trade.

If you need to purchase wine at the time of vintage, for the needs of your household for the entire year, because later the price of wine will go up, you are allowed to buy it on Chol Hamoed,⁸ 539:31) but it is forbidden to buy it for business purposes.⁹ and Ramah 539:9. Eliyahu Rabbah rules that buying wine in order to profit is permitted, and only buying large quantities for your own use is prohibited because it is an unnecessary bother. See Biur Halachah who says not to protest against those who rely on this opinion.

footnotes: ⁸ You may not purchase more than one year’s supply because it can be purchased again the following year. (Beis Yosef, Bach, Mishnah Berurah ⁹ See Shulchan Aruch

Things that are needed for the Yom Tov, like fruits and spices,¹⁰ 539:10 permits their sale because they are perishable. Magein Avraham and Mishnah Berurah include non-perishable items as well, provided they are obviously for Yom Tov needs. Anything for Yom Tov that is not obvious, must be done in private. (see Shulchan Aruch 533:5) may be sold regularly, even openly. And since you are allowed to open your store to sell to a Jewish customer, you may also sell to a non-Jewish customer.

footnotes: ¹⁰ Shulchan Aruch

It is customary to be lenient about collecting debts, even when the debt is owed by a Jew, because we consider this the prevention of a loss.¹¹ 539:2–3. This reason is only necessary for commercial debts such as payment for merchandise (already delivered). These have the halachah of commerce, and are allowed only when classified as prevention of loss. Debts from loans, however, are not considered business and you may try to collect them on Chol Hamoed, even in court. (see Taz, Mishnah Berurah 539:7–11) If you have a good security (מַּשְׁכּוֹן) you may not make your claim in Beis Din (court) on Chol Hamoed. (Eliyahu Rabbah) When claiming outstanding loans, etc., if they are not considered prevention of loss, you may not do melachah (like writing) in the process.

footnotes: ¹¹ See Shulchan Aruch

Lending money on interest to a regular non-Jewish customer is permitted, because it would be a loss, if he took his business elsewhere.¹² If you lend money to a non-Jew, who is not your regular customer, you should spend the interest¹³ of one week for [the mitzvah of] rejoicing on Yom Tov.¹⁴ 539:45) Selling merchandise to someone who is not a regular customer is forbidden, and it is of no avail even if you spend more of your profits for [the mitzvah of] rejoicing on Yom Tov.¹⁵ 539:17, Mishnah Berurah 539:45) But you are permitted to sell to a regular customer, because it is considered prevention of a loss, so that he will not get accustomed to purchase elsewhere.

footnotes: ¹² Rabbeinu Tam, Rosh. ¹³ If it was a large loan and you find it difficult to spend so much, you should do the best you can. (Ba’eir Heiteiv, Maharil) ¹⁴ This is in addition to what you had intended to spend. (Mishnah Berurah ¹⁵ See paragraphs 1–2 and footnotes 4–5. Lending is less restricted than business because it does not involve the bother of pricing or the disappointment of overpaying. (Magein Avraham

It is forbidden to exchange money¹⁶ 539:14. Because it is considered business. (Vilna Gaon, Mishnah Berurah 539:47) (on Chol Hamoed).

footnotes: ¹⁶ Shulchan Aruch