When he vacated the property and returned to his home state, he left under hostile circumstances and left significant damage at the house.

As always, your tax professional should help you navigate these rules and apply them to your specific circumstances as with all tax law, there are caveats and nuances to everything which need to be examined!

I imagine that some DSTs are failing, but the question is how prevent that is, and what are the circumstances of those DSTs in trouble versus those that are meeting their return expectations.

Simply can't.Everyone thinks that a circumstance (like being in foreclosure, tx liens, or .. ahum... distressed property) implies motivation.

It can be extremely stressful especially while your down payment is held in escrow and you're only receiving 2nd hand updates.Do you know under which circumstances you'd be able to back out of the deal and retain your deposit?

Motivation is an emotional response to a circumstance, not the circumstance itself.Someone in foreclosure, job loss, tax liens, are all circumstances.

Yes, having the court impose a constructive trust on the assets is the remedy for a claim (under these circumstances) for unjust enrichment. 

From an outside viewer, I would be nervous to work with either one of you, since you are fast to go public with any grievance and the realtor has poor communication skills and has no problem blaming external circumstances for lack of a simple courtesy call.

Of course there could be other circumstances specific to you that change your analysis, but what you laid out is correct.

Can I ask if you've been using a property manager and what circumstances led to the properties being mostly vacant?