This is pretty simple.
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Amount shows on the terminal for your approval (much like a debit transaction). You press Yes (green) to accept, or Cancel (red) to decline.
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The problem is that bitcoin is a push system. If the shop can directly charge bitcoins in your address it's because they know your private key...
Exactly. It's not as easy as a credit card unless there is going to be some sort of "bank" to hold the bitcoins for you and send them to the shop.
The problem is that bitcoins can't be moved from an address without a signature from a private key. Do you put the private key on the card? In that case, anyone (or any device) that has ever had access to the magstripe has the potential to store that information and then steal the bitcoins later. Of the hundreds or thousands of places that you've swiped the card, you wouldn't know which one was the thief. That's putting a LOT of trust in the merchants. If a merchant is running into financial difficulties that you don't know about, they are going to have a huge incentive to start storing private keys that they can empty at a later date.
in this situation this is not a good idea its just if we have bank for bitcoin and then do through this all its better and safe way to use these cards every where