Gemara

(Beraisa): If Shimon took back his garment from a craftsman, and saw that it is someone else's, Shimon may use it until the owner comes for it;

If he took back someone else's garment from a mourner's house or a drinking house, he may not use it.

Question: What is the difference between the cases?

Answer (Rav citing R. Chiya): One often tells a craftsman 'sell my garment.'

(R. Chiya brei d'Rav Nachman): This is only if the craftsman returned another's Keli, but not if the craftsman's wife or children did so;

Even when the craftsman returns it, this is only when he said '(take this) garment', but not if he said 'your garment.' (Then, surely he thinks that he is returning Shimon's.)

Bava Kama 114a (Mishnah): If tax collectors or Listim (thieves) took Reuven's donkey or garment and gave him a different one, Reuven may keep it, because the owner despairs.

Rishonim

Rambam (Hilchos Gezeilah 6:6): If Shimon (mistakenly) took back another's garment from a mourner's house or a drinking house, he may not use it until the owner comes and takes it. If he received back another's garment from a craftsman's house, if the craftsman's wife or children gave it to him, or the craftsman returned it and said 'take your garment', he may not use it until the other will return and take his. If the craftsman said 'take this garment', he may use it until the owner comes and takes his. Perhaps it is the craftsman's, or the owner told the craftsman to sell his garment. The same applies to all similar cases.

Rosh (3:47): We assume that Reuven told the craftsman to sell his garment, and the craftsman mistakenly sold Shimon's garment. When Shimon claims his garment, the craftsman realized his error and gave to him Reuven's. Therefore, Shimon may use it, like a buyer uses what he bought.

Question: Why may Shimon use Reuven's garment? If the buyer will not like Shimon's garment, he can return it (and Shimon will get it back), and Shimon used Reuven's without his Da'as (consent)!

Answer (Rosh): Since Reuven sorely needed money and sold his garment, he agrees that others use it, for also Reuven used the money.

Nimukei Yosef (25a DH v'Su and Rashbam DH Omar): We assume that someone (Reuven) told the craftsman to sell his garment, and the craftsman mistakenly sold Shimon's, and knowingly gave Reuven's garment to Shimon until he can get Shimon's garment back to him.

Terumas ha'Deshen (319): A Nochris launderer received garments from Reuven and Shimon. Reuven got back the correct number of garments, but later noticed that one sheet is not his, and Shimon said that he is missing two sheets. She says that she returned everything. Shimon told Reuven 'the sheet that is not yours, it is mine', and he gave superb Simanim. Reuven says 'she gave it to rne in place of mine. I will give it to whoever returns mine to me.' We do not accept his claim. Since he knows that it is not his, and Shimon gave Simanim, surely she stole Reuven's and gave to him Shimon's in place of it, intentionally or mistakenly. This is like the Mishnah in which Listim took Reuven's garment and gave to him a different one. He may keep it only because the owner despairs. When there is no despair, like in this case, if the Gazlan gave compensation, the victim may not keep it. Also, if a craftsman returned to Ploni another's garment, he may use it until he gets back his, because one often tells a craftsman to sell his garment (Bava Basra 46a). Rashi says that we assume that the craftsman sold the garment of David, who requested this, and mistakenly gave to the buyer the garment of Ploni, who did not request this. When Ploni demanded back his garment, the craftsman realized his mistake, and intentionally gave to him David's garment, for Ploni to use it until the craftsman will return Ploni's garment from the buyer. We do not say so about a garment switched in a mourner's house or drinking house, or if the craftsman's wife or children returned the garment, or even if the craftsman returns it, but he said 'your garment.' The Rashbam never allows one who got another's garment mistakenly to use it. All the more so he may not keep it! This is when it was mistakenly switched, and all the more so if a Gazlan took it! Here, perhaps the launderer ruined Reuven's garment, and stole Shimon's and gave it to Reuven because she likes or fears him more. Do not say that one may use it until getting his back, but the Beraisa forbids when it was a mistake, for then he must wait to get back his own. If so, the Reisha should have said 'Shimon may use it until the owner comes and he will return his (Shimon's) to him.' Rather, it says 'until the owner comes to take it', which connotes that he takes it whether or not he returns Shimon's. This is not only if Reuven knows that the sheet is not his, rather, even if he is unsure and Shimon gave superb Simanim. The Simanim show that Reuven's got Shimon's garment through a mistake or theft, and he may not keep it.

Rebuttal (Bach CM 136 DH uv'Trumas and Shach 1): The simple reading of the Sugya connotes that Shimon may use the garment until he gets back his. Tosfos (DH v'Chi) says so. The Terumas ha'Deshen's Diyuk (it says 'until the owner comes to take it', not 'until... he will return his to him') is invalid. However, this is only when Shimon knows that his own garment was not lost, rather, someone else has it. If Shimon's was lost or stolen, surely he may not keep (until he gets back his) what he got in place of it

Poskim

Shulchan Aruch (CM 136:1): If Shimon took back his garment from a craftsman, and saw that it is not his, he may use it until the owner comes for it. This is only if the craftsman returned another's Keli, but not if the craftsman's wife or children did so. Even when the craftsman returns it, this is only when he said Stam 'here is (a) garment', but not if he said 'here is your garment.'

SMA (1): When the craftsman said Stam 'here is (a) garment', this shows that he knows that it is not Shimon's. We do not permit this when the craftsman's wife or children returned it, even if they said Stam 'here is (a) garment', for presumably they do not know that someone asked to sell his garment, and they were merely imprecise (they meant 'your garment').

SMA (2): The Tur explains that if Shimon received a garment worth more than his own, when the owner comes, Shimon gives to him the excess, or he returns the garment and receives the value of Shimon's garment that was sold. Shimon decides, for the owner told the craftsman to sell it and did not demand that he keep it. If the owner says that he did not ask him to sell it and he was not paid for it, he is believed to take it back if he has witnesses that it was his or he gives a Siman. We assume that he asked the craftsman to sell it when it is a Safek, but not if the owner makes a Vadai claim. Shimon demands the value of his garment from the craftsman. The owner gets his even if Shimon's garment was lost. The Rema's comment (in Sa'if 2) applies also to this case.

Shach (2): The owner takes it back through witnesses even if witnesses did not see that Shimon has it, and we know only through Shimon's admission, even though the craftsman would have been believed to say that he bought it because he has a Migo to say that he returned it.

Shulchan Aruch (2): If he took back someone else's garment from a mourner's house or a drinking house, he may not use it.

Rema: When the owner comes, he must return the garment, even though his was lost. The same applies to a Nochris who launders for the Rabim and returned to someone another's garment.

Mordechai (Bava Kama 140): One may not keep what a launderer returned to him, because the owner did not despair. He pursued the launderer to return his! There was no enactment for the market (to allow a buyer to keep what he bought even if it is found that it was stolen) when a thief paid a debt with theft. There is an enactment if the launderer gave the stolen garment for collateral.

Taz: According to this, if one received another's sheet from a launderer and does not know whose it is, and it was with him so long that the owner should have sought it, surely we conclude that he despaired and the launderer gave to him something in place of his. The Terumas ha'Deshen discusses only when someone else claims that Shimon received his.

Rebuttal (Ketzos ha'Choshen 2): One acquires through despair only if Shinuy Reshus cam afterwards! Even if the launderer gave to the owner something in place of his, the owner gets back his initial garment. Also, perhaps the launderer claimed that Ones occurred, and did not give anything to the owner! The Mordechai means that the owner did not despair before Shimon got it.