Siman 20

We learn in Menachot (43a): The Rabbis taught: One who purchases a garment with tzitzit from the market from an Israelite—it remains in its status of presumptive fitness. From a Cuthean merchant—it is kosher. From a commoner—it is invalid. And even though they said a person is not permitted to sell a garment with tzitzit to a Cuthean until he unties its tzitzit, see there. And in purchasing from an Israelite there is no novelty, for all Israelites are trusted when they are not under suspicion, as is explained in Yoreh Deah siman 119. And it appears to me that the novelty is that even though tekhelet is not purchased except from an expert, as is stated there previously and as I wrote in siman 8—this is regarding tekhelet alone. However, a garment with tzitzit may be purchased from any person, and it remains in its status of presumptive fitness that whoever made this garment purchased the tekhelet from an expert (and see the Bach, and his words require further study). And the Tur and the Shulchan Aruch who wrote this law, even though now we do not have tekhelet and there is no novelty in this, nevertheless they transcribed the law of the Gemara according to their holy custom.

And from a Cuthean merchant it is kosher, for a merchant will not damage his reputation, and he certainly bought it from an Israelite and it is kosher (Rashi). But from a layman—it is invalid, for perhaps it was made not for its sake (ibid.). And it is not specifically that he is a merchant of tallitot, but even if he is a merchant of other things—he is also trusted. And there is one who questioned: how is "not damaging his craft" relevant here regarding a matter of prohibition? For "damaging his craft" applies to a matter where the physical merchandise is bad, such as muries in which they mix vinegar, and not in a matter of "not for its sake" where there is no physical difference. For if not so, we would permit taking meat from a Cuthean when he says that he bought it from an Israelite. And for this he wrote that only regarding a tallit do we act leniently, because it is not their way to make tzitzit on a garment. But tzitzit—it is forbidden to buy even from a merchant (Magen Avraham subsection 1). And there is one who forbade for another reason to buy tzitzit from a merchant: that specifically when he sells a tallit with tzitzit, where the primary profit is from the tallit—he is trusted regarding the tzitzit for the reason that he will not damage his reputation. But not when he sells the tzitzit alone where the profit is from the tzitzit, for in this he is not trusted for the reason that he will not damage his reputation (Taz subsection 1). (And there are those who say that when one buys from a merchant—one must untie the tzitzit. And it is not compelling.)

In my humble opinion, it is explicitly implied from the language of the Baraita that it cited a tallit as a greater novelty; for even though they said a person is not permitted to sell a tallit with tzitzit to a Cuthean, nevertheless he is believed (and so wrote the Eliyah Rabbah). Therefore, our teacher, the Rema, was precise to say that if the merchant says he bought it from an Israelite, he is believed. Thus far his words. And his intention is also this: for if not so, he does not damage his reputation at all, as he could say, "How was I to know that it requires 'lishmah'?" and the merchandise is good. Therefore, one must say that if he says he bought it from an Israelite, he is believed, meaning that he spun them, twisted them, and hung them lishmah. And since he is a merchant, he will not damage his reputation by lying in his speech. And as for the fact that we do not take meat from a merchant, there is another reason for it: because the sages forbade meat that was hidden from the eye. But certainly this law also applies to tzitzit alone. Nevertheless, in practice, it is difficult to disagree with the great Acharonim.

And this, that one may not sell a garment with tzitzit to a Kutite, the reason is lest he accompany an Israelite on the way and kill him, or that he give it to a harlot as her hire, and they will say: "An Israelite gave it to her" (Gemara Menachot ibid.). And it is forbidden to sell even to a merchant, not like there is one who is lenient in this (Magen Avraham subsection 2). And know that we say in the chapter "Ein Ma'amidin" (39a) that tekhelet may not be sent via a Kutite except with two seals like meat and milk. And some have written: specifically tekhelet whose price is expensive, but our tzitzit—one seal is sufficient. And some say: since it is a Torah prohibition, two seals are required (Magen Avraham subsection 1). And this is specifically when there is a concern that he benefits from the exchange. But otherwise there is no concern, for he is not suspected of causing others to stumble. And such is the law regarding a suspected Israelite, and likewise when depositing with them, and the details of these laws are explained in Yoreh Deah siman 118. And there is one who says that it is possible that when they are spun and cut—it is permitted (ibid.), for the matter proves that they are tzitzit. And just as one may not sell a garment with tzitzit to a Kutite, so too one should not give a garment as a pledge to him when it has tzitzit, and likewise one should not deposit it with him. Unless he deposited it temporarily, for there is no concern for these suspicions that have been explained.