Is it permissible to use an unsecured credit card (MasterCard) in the manner described to avoid usurious increases, and is it permissible to guide friends to use it for the same purpose?

It is permissible to use a Visa card if it is free from শরীʿah prohibitions, such as topping up the balance first and then using it for purchases. It is stipulated that one must not enter into a contract that includes a usurious late fee, except out of necessity and with the ability to pay within the grace period. It is permissible for the bank to take a commission from the seller, and scholars have differed on the permissibility of charging it to the buyer. There is no harm in recommending it to friends if it is free from শরীʿah prohibitions.