Its a Yahoo system, they handle all of the charging, the seller does not see any credit card information, as far as I know (thats how it used to be with yahoo shops a few years ago)
Remember, if they charge you, then they enter a binding contract to ship you the item.. they can cancel the order any time before charging you, but once that happens, the gig is up.
The only way they can back out then, is if you agree for them to refund you, if you do not agree, then they must hold up their end of the bargin.