That isn't a harder problem. It's a much much easier problem. YOU can decide where to buy from. It's a much saner system from both the customer and the seller's perspective.
And it works right now. In the Netherlands there is a system called iDEAL that works like this:
1. You go to a seller's site e.g. bol.com (which is like amazon).
2. You fill your cart and click checkout.
3. You get sent to your bank's site with a page that displays the amount and a button "pay".
4. The bank then transfers the money to bol.com.
They stated as a design goal that you shouldn't be able to back out of a transaction once it's gone through. The problem was that the system became popular with sellers of fraudulent goods, and this does, eventually, start to cause problems.
I suspect that iDEAL has some way of letting you report fraud and get a refund from your bank if you get ripped off. they probably have some form of chargbacks, etc.
It works like wire transferring money to the seller, you get the same rights and protections. In fact it is wire transferring money to the seller.
Charging back is not easy, but it is not a problem in the least. It's only a problem when you buy from people you don't trust (but then I wouldn't want to give them my credit card number at all!). This does happen on sites like ebay. The risk is moved from the seller to the buyer. For sites like ebay you need a middle man to be safe, only now you need it as a buyer instead of as a seller.
And it works right now. In the Netherlands there is a system called iDEAL that works like this:
1. You go to a seller's site e.g. bol.com (which is like amazon). 2. You fill your cart and click checkout. 3. You get sent to your bank's site with a page that displays the amount and a button "pay". 4. The bank then transfers the money to bol.com.