The Mishnah in Pesachim (53a) tells us:
ד,ג מקום שנהגו למכור בהמה דקה לגויים, מוכרין; מקום שנהגו שלא למכור, אינן מוכרין. ואל ישנה אדם, מפני המחלקות. בכל מקום אין מוכרין להן בהמה גסה, עגלים וסייחים שלמים ושבורים. רבי יהודה מתיר בשבורה; בן בתירה מתיר בסוס
In a place where [the people] were accustomed to sell small livestock to gentiles, one [may] sell [them. In] a place where [the people] were not accustomed to sell [them due to certain concerns and decrees,] one [may] not sell [them. However] in every place, one [may] sell [to gentiles] neither large livestock, [e.g., cows and camels, nor] calves or foals, [whether these animals are] whole or damaged.
[The sages prohibited those sales due to concern lest the transaction be voided or one side reconsider, creating retroactively a situation where a Jew’s animal performed labor for a gentile on Shabbat in violation of an explicit Torah prohibition.]
Rabbi Yehuda permits [the sale of] a damaged [animal because it is incapable of performing labor.] Ben Beteira permits [the sale of] a horse [for riding, because riding a horse on Shabbat is not prohibited by Torah law.]
The Koren notes:
The Sages prohibit selling large animals to gentiles due to the concern that a Jew’s animal might perform labor on Shabbat. It is permitted to sell the animal through an intermediary, since the concern with regard to desecrating Shabbat no longer exists.
I find this most curious. Who is this intermediary? If he is Jewish then surely he cannot sell on to a gentile and if he is a gentile then how can the Jew sell to him at all?
Answers on a postcard please…..