The charges you are seeing are most likely ‘Authorization checks’. An authorization charge is performed as a check to ensure the card is active and has funds in it. It is performed for security reasons and is instantly released and refunded (Although it may take a few days for this to reflect on your statement). This is stated in a pop up before you confirm the rental.
Generally, the authorization charge is a small % of the value of any skin you attempt to rent or 100% of the Prime package you select.