Does he have a public defender or lawyer you could contact? 

Check out Note Assistance Program, NAP Nation (Naked Notes Podcast).  

Any tips on financing, lenders, or programs that might work well for this type of purchase? 

See the chart from Fair Isaac Company (FICO) below: FICO Score Pct of Population Default Probability 800 or more 13.00% 1.00% 750-799 27.00% 1.00% 700-749 18.00% 4.40% 650-699 15.00% 8.90% 600-649 12.00% 15.80% 550-599 8.00% 22.50% 500-549 5.00% 28.40% Less than 499 2.00% 41.00% Source: Fair Isaac CompanyAccording to this chart, investors should use corresponding vacancy + tenant-nonperformance factors of approximately 5% for Class A rentals, 10% for Class B and 20% for Class C.To address Class C payment challenges, many industry "experts" are now selling programs to newbie investors about how Section 8 tenants are the cure.

Their program is low downpayment, low closing, no PMI, no upper income limit. 

After accepting, I was hit with (thinly) disguised solicitations as messages (“I just want your advice/feedback, can we jump on a quick call to see if you qualify for our program”) by each one.  

They batch the deposits together and you have to go deep into the program to determine which tenant made the payment, that was deposited into your account.

In other words, they cannot invest with us unless they are qualified and invited to join our program.

Correct, but according to the IRS Publication 5653 Cost Segregation Audit Technique Guide this IRS prefers an “onsite” visit.

When evaluating the deal, push for details on occupancy, lot rent, utility setup (public vs private), park-owned vs tenant-owned homes, expenses (including deferred maintenance), and any zoning or legal compliance issues.