Is there a web site or even a tool on Bigger Pockets to be able to figure that out? 

There are many others that can be found through a web search or on Meetup.com.These are a good place to meet other local investors and vendors.Good Luck!

So I am assuming these properties are not in distress (foreclosure, REO, short sale), so what would be the motivation of selling a property in the web site (or what would be a buyer's motivation to buy such a property instead of just buying a non-auction property which can be inspected)? 

Do a web search, find some meetings and meet some people.

Search on the web and you can see that there are service animal certificate sites that will provide doctors who will rubber stamp (always approve) that the person benefits from/requires the service animal.  

Do you homework on the county web sites and ensure you are not bidding on useless land such as roads, non buildable lots, etc.  

I recommend you attend some meetings (they are easy to find with a web search).

You may already be doing this but go to the county treasurers web site and download the updated list.

Save my web url - www.GregWalterRealty.com.  

Here is pic of a roof with 3 or 4 layers of shingles I found on the web.