In addition to all the great information, networking is a key component.

I personally have kept all of our houses for 3 reasons1) place holder in the appreciation - if the house goes up in the market i can capture them.2) tax shelter- any "book" loss because depreciation helps me with my taxes, and gains are shielded by depreciation3) principle pay down- Your tenant is also paying down the mortgage.The key of course is expenses.

It does look like some data mining based on key words, a link here, county records there...Always trying to sell you something extra... 

For example, you set up key word alerts. http://www.biggerpockets.com/alerts

There is likely to be more to this story.Often new owners will offer "Cash for Keys" to give an existing tenant incentive to vacate and to leave a property without causing more damage.

Lots of different options, the key is your end goal.

Research is key!!!

Starting out early is key.

The key here is you are getting that ratio because of the increased risk that comes with the property.  

My key focus right now is wholesaling.