Gemara

75b (Mishnah): If Reuven hired a donkey-driver to bring flutes or wood for a wedding or funeral, or workers to take soaking flax out of the water, or any Davar ha'Avud (he will lose if the job is not completed now), and they retracted, if there are no other workers there (to do the job for the contracted wage), he hires others for more (and those who retracted must pay the excess), or tricks the retractors.

76b (Beraisa): If Reuven hired workers and he or they retracted, the other party has only complaints. This is when the workers did not go to the worksite, but if donkey-drivers or workers went and there was nothing to carry or the ground was wet and unworkable, Reuven pays their full wage;

However, there is a difference between carrying a burden and coming without a burden. They are paid like idle workers (what one would want to receive to consent to rest from work and be idle).

(Beraisa): If it is Davar ha'Avud, Reuven hires others for more, or he tricks Shimon (the worker). To trick him, he says 'originally I promised one Sela. Now I offer you two' (but he will pay only one). One may pay other workers an extra 40 or 50 at Shimon's expense.

This is if there are no other workers there (who agree to Shimon's wage). If other workers are there, he hires them. He has only complaints against Shimon.

78a - Question: How much more may he pay others at the expense of the retractors?

Answer (Rav Nachman): He may pay up to the wages.

Question (Rava - Beraisa): He may pay until 40 or 50 Zuz.

Answer (Rav Nachman): That is when the workers left their Klei Umnos (tools of their craft) with Reuven.

Rishonim

Rif and Rosh (6:6): If the workers did not leave their Klei Umnos with Reuven and he hired others for more than the value of what the first workers did, Reuven pays the excess.

Nimukei Yosef (46b DH Aval): Regarding Davar ha'Avud, even before they started working, even though they did not deposit their Kelim and it is a mere verbal agreement, they are liable up to their wages if the price of labor will rise. The Rashba says that this is only if Reuven could have found other workers when he hired these, and now he does not find other workers, so the first caused a loss to him. If he could not have found other workers, they are exempt, for they did not cause a loss to him.

Beis Yosef (CM 333 DH Kasuv): Talmidei ha'Rashba says that regarding Davar ha'Avud, even if he could not have found other workers, they are liable, for one is not silent when he sees his money being lost. Presumably, he would have found workers through toil and adding a little to their wages. However, if workers could not find other employment (Hagahos Tur ha'Shalem 31* - and Reuven retracted), he is exempt. We do not say that they could have toiled to find work, for one can seek work all day and not find it. This is when they did not yet begin working. If they began, he must pay their full wage if they cannot find other work. The beginning of work is a Kinyan. This is why the Gemara says 'if donkey-drivers went...', for their going is the beginning of their work. Even if they could not have hired themselves elsewhere, he pays their full wage. Some say that even if workers could not have found other employment, since now they cannot find other work, Reuven is liable, even if they did not yet begin working. We say that they could have toiled to find work, just like we say that an employer would have toiled to find workers.

Nimukei Yosef (46b DH Ad): If he did not hire other workers and lost due to the delay, the retractors need not pay. They accepted (through leaving their Kelim) only for the loss of hiring other workers.

Rambam (Hilchos Sechirus 9:4): If Reuven's workers retracted from Davar ha'Avud, e.g. his flax must be removed from the water it is soaking in, or he hired a donkey-driver to bring flutes for a wedding or funeral, whether he hired standard workers (e.g. by the day) or Kablanim (they accepted to do the task for a set wage), the workers can retract only if Ones occurred, e.g. illness or death of a relative. If they retracted without Ones, Reuven hires others for more at the expense of the retractors or tricks them. To trick them, he says 'I hired you for one. Take two, and finish the job', and he gives to them only what he initially promised. Even if he gave to them two, he takes back the addition. To hire others at their expense, he hires others workers to avoid a loss. Whatever he pays the latter workers more than he promised to the retractors, he takes from the retractors. If he had money of the retractors, he may pay the latter workers up to 40 or 50 Zuz per day per worker, even though the worker received only three or four. This is when he cannot find other workers to finish the job for the initial wage. If such workers are available, he hires them and has only complaints against the retractors. For a standard worker, we estimate the value of what he did. If he was a Kablan, we estimate the value of what remains to be done.

Hagahos Ashri: It seems that if the retraction caused a loss, the retractors must pay due to Garmi, just like an employer who caused a loss to workers. He is liable even for words without a Kinyan. However, Reuven may take from the retractors up to their wages to pay extra to the latter workers, and if he had the retractors' money, up to 40 or 50. If this is due to Garmi, it should apply even if Reuven does not have their money! Rav Nachman collects for Garmi! We must say that this is when the retractors caused no loss to Reuven, e.g. the flax was already soaked and when he hired these, there were no other workers to hire. Nevertheless, since he hired them, if they do not finish he can trick them or hire others at their expense. Even regarding flutes and wood for a wedding or funeral, in which there is no monetary loss, he can trick them or hire others at their expense.

Terumas ha'Deshen (329): If a worker retracted due to Ones, even if the job was Davar ha'Avud, he receives according to what he did. A Kablan receives according to how much it will cost to finish the job. If a rich person and his wife are not used to labors, if they hired a servant this is like Davar ha'Avud. This requires investigation. Workers need not pay for a non-monetary Davar ha'Avud, for Garmi applies only to money.

Poskim

Shulchan Aruch (CM 333:6): To hire others at their expense, he hires others workers to avoid a loss. Whatever he pays the latter workers more than he promised to the retractors, he takes from the retractors up to their wages. If he had their money, he may pay the latter workers up to 40 or 50 Zuz per day per worker, even though the worker only received three or four.

Rema: If he did not hire other workers, the retractors need not pay for the loss he suffered. Some say that the Heter to pay the latter workers up to 40 or 50 Zuz at their expense is only when he has their Kelim, but not when he has other things. This applies only to Davar ha'Avud that is not money, e.g. a teacher or similar matters, but if there is a monetary loss, the retractor pays the full loss.

Mordechai (349): A case occurred in which a teacher retracted after six days. He had left his Sefer for security with Reuven. Reuven needed to hire another teacher for more money, and wanted to collect the excess from the Sefer. Rabbeinu Meir said that he cannot, for it is more than his wages. We permit up to 40 or 50 only when a worker deposited his Klei Umnos, for then Reuven is more confident that the worker cannot work elsewhere. It seems that Rashi, the Rivan and R. Chananel agree.

Darchei Moshe (5): It seems that the Tur and Rambam disagree. Terumas ha'Deshen (329) rules like Rabbeinu Meir, but only regarding a Davar ha'Avud that entails no monetary loss, such as a teacher. If there is monetary loss, he must pay the entire loss due to Garmi.

Beis Yosef (DH v'Chosav ha'Ramban Zal): The Ramban says that even though before depositing their Kelim it is a mere verbal agreement, they are liable up to their wages. They resolved like this from the beginning; there is no way to make a Kinyan. However, if he did not hire other workers and lost due to the delay, the workers do not pay. They did not accept upon themselves to pay. As long as they did not become Shomrim, they are exempt even if they were negligent.

Shach (38): When they did not deposit their Klei Umnos, Reuven can seize something else only up to the value of their wages. Normally, one can seize anything.

Shach (39): The Rema understood that the Nimukei Yosef exempts workers regarding Davar ha'Avud when there is no monetary loss. Really, the Nimukei Yosef exempts even when there is monetary loss. I say that there is no argument. The Nimukei Yosef and Ramban discuss when Reuven could have hired others, just he delayed, therefore, the workers are exempt. Hagahos Ashri and Terumas ha'Deshen discuss when he could not find anyone to hire, or the loss occurred immediately.

Gra (40): The obligation is due to Garmi. The Nimukei Yosef disagrees, but the Rema holds like him only when the loss is not monetary.