First you need to see where you are shopping really. I mean you yourself stated that in case of amazon or eBay they will solve the problem on their end. Well, in this case what they are actually doing is, they are holding the payment in their account before they can pay to the seller. This way they make it sure that they don’t provide the fraud services. I mean if seller don’t sell the item then simply the money will be returned to you which they are holding for you.