Double spend attack by sending higher fee transaction directly to the pools possible? The standard client prioritizes TXs by the time of receipt, e.g. a conflicting transaction will not be relayed. This is not enforced by the network, though. Is there anything that would prevent this scenario from happening with 0-confirmations?:


Send 0.01btc fee TX to 0-confirmation accepting merchant.
Receive digital good.
Send 0.02btc fee TX directly to "all" the major pools/miners.
Miners will include the higher fee TX because they make more profit from it. (Not sure they currently do that but they could.)
brag about successful double spend


Is there anything but worry about their reputation keeping pools/miners from dropping lower fee TXs in favor of higher fee TXs?
If a merchant accepts 0-confirmation transactions, he has to accept that the transaction can be reversed. So he only should do that if he trusts you for more than the amount you transferred to him. You won't get any bragging rights for doing that, since Bitcoin never promised to be secure without sufficient confirmations.

That trust may come from different sources. For example he might know your name, and will sue you for lack of payment. Or you put an amount that exceeds the payment into escrow.

Or perhaps he just doesn't care. For example for many digital goods(most software, movies, music,...), you have negligible marginal costs, and you're already relying on the user being honest enough to not download a copy from Pirate Bay without paying you.



Personally I believe those attacks are irrelevant, since Bitcoin isn't well suited for small fast payments in the first place. I expect those to be handled by higher level protocols, with Bitcoin itself being used to handle larger balancing payments and as a secure value store.