Would the thief's act of setting up mediation advertisements to sell the cars of the one from whom he stole, the value of which exceeds what he stole, be considered a repayment of the stolen money, especially since the thief did not stipulate a wage for this work?

The validity of repentance is conditioned upon restoring injustices to their rightful owners or seeking their absolution. If the stolen items are money and it is difficult for the thief to inform the owner, or if he fears corruption by informing him, then he is not obliged to do so. Rather, he should return the money by any possible means, such as depositing it into his account or giving it to someone who will deliver it to him. If he does not know the owner or his whereabouts, then he should give the value of the stolen items in charity on his behalf. As for advertising and mediation, you are not entitled to a fee unless you are known for undertaking this work for compensation. In that case, you are entitled to a fair wage, and it can be considered in exchange for the stolen items without informing the owner. Otherwise, you are not entitled to anything, and you are obliged to return what you stole by the easiest available means.