Does selling dollars via check at a higher price and exchanging them for cash at a lower price, or buying dollars for cash and selling them via check at a higher value with the aim of profit, fall under the category of usury (riba)?

It is permissible to buy and sell dollars with a certified check or local currency, provided that the exchange takes place in the same sitting. If the certified check does not have an available balance for withdrawal, it is treated as a post-dated check, and thus, the legal requirement of immediate possession is not met. As for selling a certified check with an available balance for less than its face value, it is not permissible if the currency is the same, as this falls under usury. However, it is permissible if the currencies differ, provided it is hand-to-hand.