How do I know how much of a bid I should put in on a

pre forclosure? Is what is owed relevant? how do I understand the best bid?

When making an offer on a short sale it will need to be for more that the total amount due for all outstanding debt on the property - OR - you will need lender approval for a “short-sale”. With the majority of foreclosures requiring lender approval these days I personally think this is a tough way to invest right now.
That said, I do believe in contrarian strategies. Two years ago there were all kinds of investors chasing these, now there are very few. yet there are probably as many deals with equity now, as there were a few years ago thanks to the Five D’s of Foreclosure. Our service can really help you find these. I’d especially keep an eye out for old loans.
P.S. I’m going to move this to the investor section.

I am agreed with Sean.