How do you double spend? When I lose my account is at zero. Please excuse my ignorance if this is readily apparent and I am not getting it.
Cwil wrote a good explanation of how a double spend could work.
Sure, I'll explain it. You control two addresses, A and B. A has some balance. You create a transaction with some casino that credits your balance with 0 confirmations as the recipient which we'll call Tx1. You create another transaction using the same inputs as Tx1 with B as the recipient which we'll call Tx2. Broadcast Tx1. As soon as the casino credits your balance, you place a bet. If you win, wait to confirm and withdraw. If you lose, broadcast Tx2.
This won't work most of the time, because all things equal, Tx1 will propagate through the network quicker.
To make it work better, include a below standard or no fee in Tx1, and a normal or above average fee in Tx2. Include a blacklisted address in Tx1 like satoshidice but not Tx2 and broadcast Tx2 directly to a miner that utilizes a blacklist (referring to LukeJr here, though not sure if he still does this). If the site runs its own node, you could peer with that node, broadcast Tx1, and then utilize some kind of dos attack in combination with the double spend attack to increase your chances.
There's still luck and timing involved, but with the 1% or less edge many casinos are running these days, it could be enough to push a game +EV.
