Flip houses? Try flipping mortgages. The trade in delinquent notes has exploded since the financial crisis as government entities like Fannie Mae and Freddie Mac fuel the fire.

Fannie and Freddie sell billions of dollars worth of delinquent notes to big institutional investors, who then sell them to other, smaller investors who flip them in turn, MarketWatch reports.

Thousands of notes are bought and sold for a fraction of the value of the homes they secure, and the new owners can then renegotiate with the homeowner—offering a “cash for keys” payout and seeking a new tenant or foreclosing.

Some observers consider the situation ripe ground for potential abuses while others see it as an opportunity for investors to “be the bank” for people with mortgage problems. [MarketWatch]