are stating is that the relatively high fixed operating costs for a lower rent class C (& certainly D) properties of this size essentially render them worthless since expenses will typically exceed income (negative NOI).   

Do you have a rendering that you can share of the new design?

One thing you may want to do is find a site planner to draft something up or some renderings for you, it will cost you a few bucks but it will entice developers more so they do not have to spend any money out of pocket to understand what can be done.

However it rendered our loan worthless since there was no equity and had to write it off.

My understanding in Texas is that it is not a "official tax lien loan" unless you get a judge to render it. 

It means that the taxes owed when the judgment was rendered was $13,000, but it may have taken them a long time to notify everyone who had an equitable interest in the property and the taxes that have accumulated since then plus the administrative costs may be the difference. 

It is also possible that it took a long time since the judgment was rendered to get it to the sale and you could owe a few years of taxes if the judgment was several years ago.  

I render my services to those who don't want to deal with a realtor.

As an example, I often see home grown contracts in my state by individuals making a private loan that have no interest rate which could/would render the note unenforceable in my state.

The issue, AirBNB claims, is that the host I referred, after creating his listing, made the mistake of connecting his new listing to a property management software, and because it is 'API connected', it renders the referral as ineligible for a payout.