Learn about buying notes?

[Sequan]

When I knock on doors alot of them are vacant.

A guy told me if they are vacant I should try to get a discount form the bank. Buy the note, not a short sale.

Now if I do that, say get a 30,000 discount on a 100,000 house what happens.

Will it still go the auction?
If noone buys it at the auction, will I own the house without a payment since I am the bank?
Then can I sale the house?

I trying to figure out what is the badside to this, because it this is true it seems like a real good thing to do?

How can I learn about buying notes?