And, wow, it works for the rental company!

It sounds like he stamped his name on a company to help promote it. 

A partner of mine who worked for a RE development and research company says they regularly used Yimby data for studies. 

One of the mortgage companies has approved me, subject of course to an appraisal.

I don't want to go to a company like h&r block, but none of the indie people have reviews or reputations. 

If the AC is not working you will need an HVAC company to come out and tell if it's fixable or needs to be replaced.To be honest, everything you are saying indicates you are going to create a money pit for yourself.

If he agrees to the lease then continues to do this, fine him and follow through on eviction proceedings if he doesn’t pay and cure the problem.

Do we write a check and have the Title company hold it until work is complete?

Another angle you could consider is to diversify into different asset classes to reduce your risk, potentially continue your low tax burden and earn cashflow passively through 1031 exchanging into Delaware Statuary Trusts (DSTs). 

*Insurance company came by, did an inspection and stated the property was vacant.