Gemara

(Mishnah - R. Meir): If Reuven gave wool to Shimon to dye red, and he dyed it black, or vice-versa, Shimon pays him the value of the wool he received.

Inference: He must hold that Shinuy Koneh. If not, he should pay for dyed wool!

98b (Rav Asi): If a carpenter was given wood to make a chest, and he broke it, he is exempt, for Uman Koneh bi'Shvach Kli (a craftsman acquires the improvements he makes to a Kli).

99a (Beraisa): If Reuven gave his garment to an Uman (Levi), who returned it during the day, if he does not pay before sundown, he transgresses Lo Talin.

If Uman Koneh bi'Shvach Kli, why does Reuven transgress? (Levi acquired, and sold it to Reuven. Reuven does not owe wages, rather, for a sale!)

Rejection: Levi is paid a set wage for each time he presses it. Only a Kablan (a worker contracted for an entire job) is Koneh bi'Shvach Kli.

(Rav Sheshes): One transgresses "Lo Salin" for withholding wages of a Kablan.

Suggestion: Rav Sheshes argues with Rav Asi.

Rejection (Shmuel bar Acha): Rav Sheshes discusses one hired to deliver a letter (there is no improvement to acquire).

(Beraisa - R. Meir): If one said 'make this metal into rings for me, and I will be Mekudeshes to you', once he makes them, she is Mekudeshes;

Chachamim say, she is Mekudeshes only when she gets (additional) money.

Suggestion: They argue about whether or not a loan (what she owes him for his labor) can be Mekadesh. Both Tana'im hold that wages accrue continuously from the start of the job until the end, so they are like a loan that she owes to him.

Rejection #1: No, all agree that a loan cannot Mekadesh. R. Meir holds that wages are due at the end. Chachamim hold that wages accrue continuously.

Rejection #2: All agree that wages accrue, and that a loan cannot be Mekadesh. They argue about whether or not Uman Koneh bi'Shvach Kli.

Rejection #3 (Rava): All agree that Ein Uman Koneh, that wages accrue, and that a loan cannot be Mekadesh. The case is, he added metal of his own, and also pardoned her debt to him. They argue about whether she intends to become Mekudeshes through his addition, or through the loan (which is invalid).

Rishonim

Rif (35a and Bava Metzia 68b): Rav Sheshes taught that Ein Uman Koneh bi'Shvach Kli. The Halachah follows him. Rava concluded that all agree that Ein Uman Koneh bi'Shvach Kli. We do not rely on the rejection of the proof from our Mishnah (there is no improvement). The Halachah does not follow Rav Asi.

Rebuttal (Rosh Kidushin 2:11): The proof (from Rava) is invalid. He wanted to show that the Tana'im need not argue about Uman Koneh. He could not say that all agree that Uman Koneh, for then all would say that she is Mekudeshes. The Ri similarly refuted a 'proof' from here that wages accrue continuously , for we could not say that all agree that wages are not owed until the end. R. Tam rules like Rav Asi. Even though the Gemara suggested that Rav Sheshes says that Bal Talin applies to Umnim because Ein Uman Koneh, unlike Rav Asi, we retracted. Perhaps Rav Sheshes discusses a letter carrier (there is no improvement).

Defense (Ran Kidushin 20a DH Garsinan): If Uman Koneh, wages do not accrue continuously. Every improvement to the Kli is not a loan. The Uman acquires it. When he returns the Kli for the set wage, it is as if he sells it.

Defense (Gra CM 306:8): How can the Rosh suggest that the Tana'im argue about Uman Koneh, i.e. and R. Meir holds that Uman Koneh bi'Shvach Kli?! If so, how did the Gemara (95b) prove that R. Meir holds that Shinuy Koneh?

Rosh (9:14): If the Tana'im argue about Uman Koneh, the Halachah follows Chachamim who say that she is not Mekudeshes because Ein Uman Koneh. If they do not argue about this, all hold that Ein Uman Koneh. However, one could say that they argue about whether or not wages accrue continuously.

Pilpulei Charifta (6): He means that one could say that they argue about whether wages accrue continuously, i.e. if he was not a Kablan, rather, he was hired by the day. Wages accrue continuously applies only to a Kablan.

Rebuttal (Gra EH 28:45 and Shach CM 306:3): If he is not a Kablan, the Rif's proof is valid, for Rava could have said that all agree that Ein Uman Koneh!

Shach: The Rosh means that Rava did not say that they argue about whether wages accrue continuously, for Rava holds that the Halachah follows R. Meir

Rosh (Bava Metzia 9:43): Rav Sheshes holds that Bal Talin applies to Kablanus, because Ein Uman Koneh. The Halachah follows him, for a Beraisa supports him.

Rambam (Hilchos Sechirus 11:3): If Reuven gave his garment to an Uman, who returned it during the day, after sundown he transgresses Lo Talin. Kablanus is like a hired worker; one must pay on time.

Poskim

Shulchan Aruch (CM 339:6): If Reuven gave his garment to an Uman, who returned it during the day, after sundown he transgresses Lo Talin. Kablanus is like a hired worker; one must pay on time.

Darchei Moshe (EH 28:8): Regarding Kidushin, the Tur says that the Rosh concludes like Tosfos (that Uman Koneh). In Bava Metzia, the Rosh brought only the Rif's opinion; he relied on what he wrote in Kidushin. Alternatively, the Rosh is stringent. Therefore, in Kidushin he concludes that Uman Koneh. Regarding Bal Talin, he brings only the opinion that Ein Uman Koneh. Regarding an Uman who broke a Kli, he brings both opinions and does not favor either. In CM 306, the Tur says that Ein Uman Koneh, so an Uman who made a Kli and broke it is liable. Perhaps the Tur means that if the owner seized, we do not force him to return it, but we would not force the Uman to pay due to Safek. Alternatively, the Rosh concludes like Tosfos, but the Tur rules like the Rif and Rambam. In Choshen Mishpat, he brought only their opinion. Regarding Kidushin, the Tur is concerned also for the Rosh's opinion conclusion. We resolve the Tur in one of these two ways. He did not err!

Taz (EH 28:28, citing the Maharshal): The Tur says that the Rosh holds like Tosfos, for he brought Tosfos' opinion last. This is wrong. In Bava Kama the Rosh brought a different proof for the Rif, but said that it can be rejected. In Bava Metzia, the Rosh explicitly rules that Ein Uman Koneh. The Tur himself rules like this regarding Bal Talin. Do not say that the Tur holds that the Rosh is stringent about Bal Talin to say Ein Uman Koneh, and stringent about Kidushin to say Uman Koneh and she is Mekudeshes. In Choshen Mishpat, the Tur obligates paying. This cannot be due to Safek! Rather, the Tur erred.

Bach (EH 28:13): The Rosh ruled that Ein Uman Koneh regarding Bal Talin. Therefore, he obligates an Uman (who made a Kli and broke it) to pay. In Bava Kama the Rosh rejected the Rif's and his own proof that Ein Uman Koneh, but surely he holds that this is the Halachah. Therefore, he did not bring the opinion of the Ri and R. Tam that Uman Koneh. Only in Kidushin, after rejecting the Rif's proof, the Rosh brought the other opinion. Due to the severity of Eshes Ish, the Rosh is stringent for R. Tam's opinion to require a Get. In Yoreh De'ah 120, the Tur says that if a Nochri Uman fixed a Yisrael's Kli, one need not immerse it (like a Nochri's Kli) even according to the opinion that Uman Koneh. I.e., we are stringent like R. Tam only for Kidushin.

Drishah (EH 38 DH Shuv): The Tur holds everywhere that Ein Uman Koneh. In the Tugrama printing of the Tur (EH), he says 'the Ramah holds that Ein Uman Koneh, for there is no loan here. Also the Rosh holds like this.' The Beis Yosef changed the text, for if Ein Uman Koneh, there is a loan! The Tur meant 'we do not rule that Uman Koneh, in which case we would say that there is no loan.' Alternatively, a marginal note added the opinion of the Ri and R. Tam, and was incorporated into the text. This misled people to think that 'the Rosh holds like this' refers to the opinion of the Ri and R. Tam.

Shach (1): The SMA (12) says that here the Shulchan Aruch is like the opinion that Ein Uman Koneh. I say that it is according to everyone (if the worker does not improve the Kli - Shach 306:3.)