It looked good on the BP flip calculator but didn't fit the 70% rule.  

I filter through 50-100 per day and get a deal or two a month.

Are there rules of thumbs governing this decision?

And if the purchase price is only $20,000 a $50 deposit might be enough or you could get away with $10 or even $0."

We did a mailing here in Indiana to 250 people with over 50% of them addressed return to sender.

If by investor friendly you mean they don't sell them for 50% of value, that's correct.

When I see the numbers some of you are talking about, $50 to $100 a month in free cash flow?

Preferred age of unit is no more than 40-50 years.

Mostly consists of Millennials entering their prime "settle-down" years who are realizing they'll never afford a home for their family in the Bay Area, and Boomers and Gen X'ers who just sold Grandpa's house in San Jose for over a million and can come out here and buy something all-cash and still have plenty of money left over to retire with.I have written more about this migration pattern here if you want to know more:https://www.biggerpockets.com/forums/621/topics/396725-millennial-migration-to-sacramento-2017---here-comes-the-rushFor some B class neighborhoods, I would recommend that you try looking in North Oak Park, Arden-Arcade, Carmichael, and the area South of 50, East of 99, and North of Fruitridge Rd.

By this time I'm thinking one 50-unit building should be able to generate this cash flow.