So if you ordered 1 (one) item from Amazon and got billed for 2 (two), and when you noticed the double charge, Amazon said, "no worries, you can keep the second item", you would be okay with that?
lol
Welcome to the shady world of Bitcoin.That analogy is wrong and you've resumed your negative posting about Bitcoin. The main thing here is that 'second item' from Amazon would be harder to sell, where in the case of Bitcoin on a exchange is instant.
What if a customer only had enough funds in his bank account to make one purchase of Bitcoins? Surely he would be charged by his bank if another attempted withdrawal took place after the first. Those charges could put his account in arrears, which he would also be charged for. Bank charges can rapidly spiral in such situations. Would Coinbase reimburse him for his bank account arrears?
Well yes, there is also that. However, I'm pretty sure that a lot of people can go into a "negative balance" (i.e. under 0;credit). The number of people that this is going to affect should be limited.