I don't think FFC (or any other store) intends to take customer's money in such blatantly obvious manner ! The problem for the stores usually is that if the first transaction seemed to not go through, they have no easy way of getting the customer to come in and pay for that invoice again at a later date.

So they would typically insist that the customer make the payment again, and if this indeed becomes a duplication, the bank would refund it later to the customer. This is how it has been done for ages, except that recently, some banks started sending customers back to the store to sort it out, which results in extreme frustration for the customer.

If you personally visit the bank, they will sort it out for you. I guess this is a small price to pay for the convenience of using charge cards, caused by network/equipment glitches/timing.