Rules around Auctioned homes

[William Sieving]

I was reading J. Scott's book, "The Book on Flipping Houses...", and he mentions something about having negotiated with a seller who needed a quick response due to their impending auction date for the property and I was surprised to hear that this negotiation was a possibility.I am new to the real estate business so it did not even occur to me that one could make an offer on a home that is already scheduled for auction. 

In what situation(s) is this a possible option and how does one go about making such offers to the various owners of these properties? Any explanation would be greatly appreciated! Thanks in advance!