What is the ruling on taking a commission as a mediator between two parties, one of whom possesses an old, abolished currency, and the other exchanges it for new currency in return for a commission, knowing that the old currency has no value except through this exchange, which cannot occur without mediation?

If a currency is abolished and no longer accepted, it is permissible to purchase it with cash, with a delay and a differential, due to the removal of the cause for usury. The abolition of dealing with a specific currency is an injustice, and the owner of the money has the right to seek to restore his right and exchange the old currency. If he is unable to do so except by paying a bribe to an employee, it is permissible for him to do so, and the sin is upon the employee. Mediation in exchange: If the second party is a responsible employee, it is not permissible for him to take a commission unless he is obstinate, in which case it is permissible to pay him a bribe, and the sin is upon him. If he is not responsible, then what he takes falls under the category of "price of influence," which is a matter of dispute among jurists. It is permissible for you to be an agent for the rightful owner and to deliver the bribe to the employee to avert injustice, but it is not permissible for you to be a broker or an agent for the oppressor. It is permissible for you to agree with the rightful owner on a fee for your agency without exploiting his need.