I'm not sure I could agree with that. If he was tremendously lucky and mined the next block including a spend from the same address, he could withhold it for a minute while he executed his double spend. But, like I said, unless he's buying a car or a house, it isn't worth the effort. And if he is buying something expensive, the seller should have his name and address anyway and can press charges, same as with credit card fraud.
We were just thinking about different price levels.$100 in a grocery shop -> 0 confirmations.
$30.000 in a car retailer -> 1 confirmation.
$1000.000 at a real estate broker -> 2 confirmations.
Yep. Double spends are ridiculously expensive to pull off reliably even with 0 confirms as long as the merchant's node is properly configured.
