VanHalenLover: In todays society of instant gratification, this would be ineffective. Check out at any major retailer today and you will see racks of pre-paid cards for sale. Too easy for someone to get multiple cards to go along with their multiple accounts. It would make it a tad more difficult, but wouldn't solve it.
You make a great point and are right, VHL,... if we were discussing gift cards. We are not.
Issued credit cards have a verifiable account number... Gift cards can be determined at the point of sale, iirc.
My solution would require a valid "issued" cc, no gift cards...
Again, it's not perfect I know. There are a lot of people that would not be able to participate in the skill gaming parts of the game as some folks just don't have/can't get an issued credit card.