I am not t familiar with Augur, so maybe that is why i do not see why it is necessary to use Augur. Also i wonder how the contract can verify the amount of fiat loaded on the debit/gift card.
You can read about Augur at
Augur.net. The value of using it as I suggested is that the contracts would be triggered by a unconnected event -- the bet. To ensure that the bet has no connection to either buyer or seller, multiple bets of the same (or nearly the same) outcome time/date could be required by the contracts. As for verifying the amount of fiat on the card, the exchange of information between the contracts would actually take place before the outcome of the bet. The Augur-validated fact of the bet's outcome would then trigger the decryption of the debit/gift card data and crypto address/keys and the sending of that data to the respective parties. So if there was not enough fiat on the card, the seller's contract would fail before the bet had completed and the seller would know this.