How does Amazon actually verify that You Have Funds on your Credit Card?

Amazon charge your credit card right before they physically dispatch your goods.

For example, imagine that you know you have zero funds available on your card. If you place an order anyway, Amazon has yet to send an email to let you know that have received the order in which they post. It has nothing to do with payment for order is only to confirm they have received the order.

When it's time for the delivery order, indeed, will try to debit your card. However, if when you are unable to make payment will be sent an email to let you know I've had a problem charging your card, and asks you to update your payment or try the same card again if I want to continue with the application. You can ignore this if you decide not to continue with the order after all.

So yes, you can not have anything on your card, but Amazon will contact you to that request.