How to determine if a pre foreclosure is a deal

[Jeet Sangha]

Pretty much what the subject line says..

What elements do I need to pay attention to see if a pre foreclosure property can yield profit. And is realtytrac a good source for pre foreclosures?

Basically I want to learn everything about it and feel confident about my numbers before I start knocking on doors.

Any bit of advice is appreciated.

I'm in California if that makes any difference.