If the income is acceptable compared to the debt payment, then that is the ratio.

For years, I was thinking I'd roll the entire amount into my Traditional IRA as I could defer taxes.

Cap rate is difficult to find in smaller communities it seams (not that much product to compare).

When I address FSBOs I'm coming from the investor standpoint to purchase their property through one of the above mentioned strategies.BUT, if they don't like those options, I can always be put on the back burner for a traditional listing when need be!

I'm good with strategies 1 or 4, and I think they offer many advantages over the traditional forms of borrowing. 

Then compare that number to the total income show on the Schedule E.

I would take both comparables and income valuations (cap rate) into consideration.

Compare your values to the actual values.

@Russell Brazil Not trying to compare status of real estate success than for any other reason than he has an entirely different opinion on solar conditions in DC/MD/VA.

Comparing these terms to the best financing I've found through a bank ($320k loan, 5.5% fixed for 10 years then refinance, amortized over 25), with same purchase price and down payment, results in a lower monthly payment by $315/mo, plus my principal balance after 10 years of payments through bank financing would be $240,000, compared to the $180,000 balloon that the seller wants at year 10.