Is it permissible for an employee to benefit from the exchange rate difference (dollar against dinar) adopted by the employer, by taking 70 dollars for 100 dinars from the customer, given that this transaction does not follow the daily exchange rate?

It is permissible for a seller to sell goods in a foreign currency and take a local currency in return immediately, even if the exchange rate differs from the market rate. The decisive factor is the agreement of the two parties and the condition of immediate possession. However, it is not permissible to sell for a deferred price in a foreign currency with the condition of payment in another currency, because it is a deferred exchange (sarf mu'ajjal), which is usury (riba), according to the Prophet, peace and blessings be upon him, who said: "If it is hand-to-hand, then there is no harm; but if it is deferred, then it is not permissible." As for an employee who does not own the shop, it is not permissible for him to take the currency exchange difference for himself without the knowledge of the employer.