Brings in $11k/month in income and $4k/mo in cash flow after all expenses (this is after verifying/questioning owner's rent roll)- 19 MHs, all POHs.

If they can't verify income then move along; nothing to see here.

If he can't provide a verifiable proof of income with references, I would pass. 

All income must be from a verifiable source.

I would start by asking a neighbor or somebody to verify they still occupy the unit.

Verify taxes with the county, check utility bills, etc.

Some people may say the biggest catch is if the company tries to scam you, but that falls under doing proper due diligence-- the benefit of turnkeys is that you have the ability to verify everything about the property prior to putting your money into it.

Again, I would consult a CPA / Tax professional to verify. 

Look for red flags like evictions, criminal history and credit score and can't verify employment. 

Authorization: Applicant authorizes Landlord and Landlord's agent, at any time before, during, or after any tenancy, to: (1) obtain a copy of Applicant's credit report; (2) obtain a criminal background check related to Applicant and any occupant; and (3) verify any rental or employment history or verify any other information related to this application with persons knowledgeable of such information."