@SUHsE I have used my debit card on various web sites, and I have never been charged twice, ever, so if you are, I would begin to question your financial institution!
I have made purchases at Amazon, Macys LL Bean, Duluth Trading just to mention a few that I have shopped at, and I state AGAIN I have NEVER been charged twice! Why would anyone in their right mind hold up two amounts on their debit card until the vendor can can verify if the funds are available, that just sound obscene! Maybe you have disposable income and can hold money for 3-5 days but I think most Americans cannot afford this when they use a debit card? With my debit card if the funds are not available, the purchase is declined, that is the only way it should be with all financial institutions, IMO!