So doing market research on rents independent of seller details, and then I assume, add a clause in the offer about current tenant rate that survives the transaction.Do you have any practical methodology for analyzing operating expenses if the owner doesn’t disclose?

This information is not about license but its more like a utilization of depreciation methodology.

You get a write-off for your interest paid right now that you would no longer get if you paid them off.I think the people who want to sleep soundly at night opt for the debt free methodology.  

So my take on it, until NAR decides some day to publish to the public their statistical data collection methodology, is that 2/3 of Realtors are renters.  

After the inspection I found out that all the AC units and furnaces will need to be replaced pretty soon due to their ancient age.

I would imagine you would need to match inside finishes while maintaining the ancient outside looks?

That, in my experience has nothing to do with accounting methodologies but instead has everything to do with good assett management.Just my two cents...

This is basic economics, finance and appraisal methodology.

In other words, if you analyze 10 deals using the same methodology and relative estimates and they all come out +/- 12% cap, then I would say that your method is consistent and can be used as a baseline to compare  your actual  purchase to. 

The amount the buyer paid for the income it produced (CAP) can be a useful comparison - provided the net income and CAP is calculated using the same methodology in all properties being compared.Smaller, 2-4 unit buildings, are residential properties, not truely multi-unit, and are valued using comparable sales.