Commercial investors  WOULD LOVE  to be able to use direct sales comparison to value properties because it is easier and MORE accurate. 

Commercial transactions are liabilities by comparison.

I export to excel, calculate price/squarefoot to get some ballparks and then pull up similar houses for a more in depth comparison.  

I did a cosmetic fix on it and walked away with a little under $30k (before tax), as a comparison.

(barring the deposits and pet rent comparison)@mike I wouldn't think written notice is necessary for not allowing pet damage

Also I'd check out Zillow's data center if you can't find any comparisons in the area.  

Be sure to work with a lender who provides a clear comparison for you.  

But by comparison, the same duplex was on sale recently for over 230k more than what it sold for 4-5 years ago (not sure what it actually sold for).

When I spoke to the president of the HOA, he told me that a 30% or better funded reserve was considered good but I don't have any basis of comparison and wanted to know if anyone had a good rule of thumb for how well funded an HOA of a 20 year building should be.

Shop around so you have some comparison.