They've been buying into the 1000s haven't they? God they must be taking massive losses. Wouldn't be surprised if they're the ones with these fake walls trying to inflate the depths for quick dumps.
SecondMarket will not lose any money, no matter what the price does. When an investor gives them money for N shares, they buy N/10 bitcoins at the current market price. When the investor liquidates those N shares, they sell the N/10 bitcoins at current market price and give him that money.
If the price went down in the meantime, the investor takes the loss; if it went up, he takes the profit. In any case, SecondMarket skims off the entry, maintenance, and exit fees.
SecondMarket could make even more money if they had a private source that would sell them bitcoins below market price. That difference in price would be their extra profit.
