You need to understand how the whole process works.
There are wrinkles in every state/city, but this is how it
generally works:
When a person falls behind on paymens on their house, the bank will typically begin a formal process to try to bring the account current again, and warn the homeowner of foreclosure proceedings.
This is "preforeclosure". Many times, the homeowner will list the house as a short sale at this point, giving up on the idea of being able to remain in the house, but trying to limit the damage of default (most states are "recourse" states meaning that even after you lose your house the bank can come after you for any deficiency).
Eventually, the bank will be unable to collect, and the house will be listed for the sheriff's auction. Typically the bank will bid on the property up to a maximum of the outstanding loan principal (and the auction usually ends much lower than that). But not always. Sometimes the bank will just let it go to a bidder.
Here's an example of a Sheriff's auction:
http://www.nj.gov/counties/mercer/officials/sheriff/informational/sale.html
Usually the bank wins the auction and retains control of the property, it is now part of the bank's Real Estate portfolio, and called a "REO (Real Estate Owned). They contract out with a real estate company to list their REO properties, and sometimes list them on their own websites. Here are some examples.
http://foreclosures.bankofamerica.com/real_estate_owned
My tip to you would be to learn
exactly how the process works in your area, and then figure out what your best angle is. Some guys like the preforeclosures, they search for short sales or drive around putting those "Cash for Houses" signs everywhere. Some guys go to every sheriff's auction and know how to find a deal. Some guys develop a good relationship with a realtor and go after REOs. There's no one answer.