I'll Take CashG 10

To unlock this achievement you simply need to sell off any unwanted Burn cards from your deck. From the lobby go to your Burn Cards menu, select an unwanted card, and hold LT+RT at the same time to sell the card. In the top right part of the screen you will see a credit value for each card. If you choose to sell the card the credit amount will be added to your Black Market Credits which are used to buy items from the Black Market. Sell off 100 cards from the deck and the achievement will be yours.