Credit Cards

Q: Most credit cards have a facility where a person is allowed to use credit up to a certain amount and if it is paid back to the back within 55 or 60 days etc then no interest is charged, however from the onset the client and the bank are fully aware that if the client fails to pay within that time limit then interest will be charged. Is it jaiz for the client to utilize this facility and pay in the money within the time limit?

Selling electricity from a vending machine

Q: I would like to find out the following:

If one has to sell electricity from a vending machine, the service provider gives you a discount of 1, 5% on the sale of the electricity.  Can one charge a customer and additional 5% on the sale of the electricity {e.g.: a customer comes to buy electricity from you for R20-00 but you charge him R21-00 for the sale.  On the customer’s slip they will see that they have only purchased electricity for R20-00.) The cost incurred by me is that I will have to pay the cash deposit fee of about 1%, a monthly unit rental fee of about R150 per month. Is it permissible to do this type of a sale?