I have a question about your Safe Purchrase example https://solidity.readthedocs.org/en/latest/solidity-by-example.html#safe-remote-purchase
In the following scenario:
1) The buyer and seller have 0 ether on their accounts
2) The buyer convert X€ into 10 ethers on his account
3) The buyer order for 10 ethers a product of the seller
4) The seller locks the transaction
5) The buyer empty his account and convert his ether into X€. There is 0 ether now on the buyer account.
6) The buyer receives the product and confirms the reception
Since the buyer have 0 ether on his account at this time, they can not be transferred to the seller? Or is that the lock to prevent the conversion € / ether?