You can't convert crypto into fiat. You can trade one for the other with someone but you cant convert them, it's not alchemy, it's just a change of ownership. Exchanges like BTC-e have bank accounts which people transfer by wire and other means funds into to purchase BTC-e "casino tokens" called USD/RUR/EUR which they can gamble and trade with other BTC-e users for fiat or crypto tokens. The bank account balance doesn't change for those trades, it only changes when people cash out their tokens or make a new deposit, or when BTC-e take their fees out, so the balance should be high unless seized. Same goes for their crypto wallets.