Is there any way to take advantage of these listings without having 20% down? 

Looking at buying a SFH in the San Fernando valley, Lake Balboa area of Los Angeles.

The most we could really pull together is $20k +/- which is more like the 3.5% we'd need for an FHA loan on $5-600k which is what we're looking at. I'd love to find a fixer upper in the area but not many left. I'm very handy and would want some sweat equity. A built in rental unit would be great too (unofficial is ok)

I do have a 3 unit rental property in Maine that I could use equity in, but I'm hesitant to spend the money on appraisal and refinancing and increased taxes. 

Looking for advice on the best process to to build equity, also I need a loan because my FICO dropped 40 points last month from 830 to 791 because of "lack of installment loans" my rental unit is owned by LLC so it's not on my credit. My fiancees FICO is 815, we make about $8k/ month.

Our only expense is rent and her student loans and utilities. Insurance is a couple hundred a year, we own our vehicles. And have been with current employers for 5+ years. 

Refinancing/bank appraisal wouldn’t affect your tax assessed value or taxes. 

Remember closing costs on an fha will be another 3-6%.  

Crap, 3-6% for closing is crazy

Your subject line said "auction " listings. You shouldn't be buying auction properties unless you know where the money is coming from.  Counting on getting a loan before the auction settlement date is usually not practical.

Also be aware, many auction listings on Zillow, Trulia, ect.  are not accurate. Many are previously settled and still erroneously listed.

Agreed, I was going to point the “auction” status is often erroneous.  If you want to buy something, talk to a lender, get a preapproval and an idea of All the costs, then you’lol know where you stand.