What is the ruling on buying dollars or foreign currencies with a certified check, where the seller receives the amount after 25 days, in exchange for the merchant raising the exchange rate by 20%?

Delivering a certified check is equivalent to taking possession if the issuer has available and withdrawable funds. The crucial factor is the actual ability to dispose of the check's contents, and a short period preceding actual possession is forgiven. However, the beneficiary of the check is not permitted to dispose of it during this period until the effect of receiving the check materializes through the actual possibility of receiving the purchase amount. The scenario mentioned in the question does not fall under this ruling because the merchant increased the exchange rate in return for a clear deferment (25 days), which indicates a delay in the actual receipt of the amount.