How to determine if there is equity in the house

[Howie Baker]

How does one determine if there is equity in a house?  I would like to help some homeowners in pre-foreclosure status by catching them up on their payments, rehabbing the home for a flip and then sharing in the profits with them.  This process only works if there is some decent equity in their home.  Is there a way for me to discover this before ever picking up the phone to contact these people?