When you complete a checkout, your credit card company puts an authorization for the order amount on your card. This money has not been paid to us, rather your card company has put a hold on it for you while you check out.
If your address information fails to validate (maybe your shipping and billing addresses aren't the same), then your payment will be declined. Your credit card company will release the Authorization between 3-5 business days after it is made depending on your bank.
If you attempt to checkout multiple times, your card will be authorized multiple times.