The Mishna teaches (75b) that kol ha-mishaneh, yado al ha-taḥtonah – whichever participant in a business deal changes the terms of the agreement is the one who loses out. The Gemara on our daf points out that this comes to support the position of Rabbi Yehuda. Rashi identifies this opinion with a disagreement in a Mishna in Bava Kamma (100b).
That Mishna discusses the case of hikdiḥo yorah – if the wool was boiled at too high a temperature and was burned – the wool is considered entirely ruined, and full restitution will need to be made to the owner. If the dye came out uneven, the owner will pay either the added value of the poorly dyed wool or the dyer’s expenses – whichever is less. If he dyed it the wrong color entirely, Rabbi Meir rules that full restitution must be made to the owner; Rabbi Yehuda rules that the owner will pay the lesser value of either the added value of the newly dyed wool or the dyer’s expenses.
The Ra’avad explains the difference between Rabbi Meir and Rabbi Yehuda as being based on two different outlooks about the relationship between the owner and the dyer. According to Rabbi Meir, by going against the instructions of the wool’s owner, he gets the status of a thief, and takes possession of the “stolen” object, for which he must pay. Rabbi Yehuda believes that he remains an employee, albeit one that does not deserve to be fully paid for his substandard work.
Regarding Rabbi Yehuda’s position, the Maggid Mishna understands Rashi to rule – similar to the position of the Rambam in his commentary to the Mishna – that the owner has the option of demanding full restitution of the value of the wool. The Rambam in his Mishneh Torah (Hilkhot Sekhirut 10:4) does not accept this position, since he rules that there is no opportunity for the worker to take possession of the object through his work – ein uman koneh be-shevah keli. Thus the owner will pay either the increased value of the wool or the worker’s expenses – whichever is less.