Years ago when i ordered from a site they had a system where they would charge you slightly less than the price on the order, but you had to quickly verify the last 2 digits. Ie a $100 item and they would charge you 99.97, and auto cancel the order if you cant provide the actual cost (from your internet banking). Since credit card charges appear instantly this was pretty simple.

I'm surprised I've never seen such a system since, it seems very effective against stolen cards.