Is it permissible for a currency exchange shop owner to transfer a sum of money for a person who pays part of it and pays the rest in installments, while taking the usual transfer fee, and is it permissible to increase the transfer fee by agreement of both parties?

It is not permissible to transfer money to someone who has not paid the full amount or has paid only a portion of it, because this combines a loan with a paid agency, which is religiously prohibited. The legal principle prohibits combining a loan (Qardh) with any contract of exchange, such as lease (Ijarah) or paid agency (Wakala bi Ajr), in order to block the means to usury (Riba). The noble prophetic Hadith, "It is not permissible to have a loan and a sale," explains this prohibition, as it includes every gratuitous contract combined with a contract of exchange, because the gratuitous act in this case is for the sake of the exchange and not an absolute donation, thus becoming part of the compensation.