He asked me if I'd rent to them again and I said I never actually rented to them in the first place, and even though they didn't cause any problems and paid the rent on time, no I wouldn't rent to them because I know them to be dishonest and were unwilling to sign a contract. 

Be unwilling to fail.

So, this reply was more to avoid having other people unwillingly fall into that trap than it was a reply to you specifically.

If the seller is unwilling, the deal cannot close. 

What we found fairly quickly is that your knowledge was limited (or you were unwilling to share), and for us to be able to succeed in the way we wanted to, we had to take the next steps and go far outside of your group.

If you delivered a clean / clear unit and the tenant has had a hand in creating a pest issue by living sloppily, leaving food out, etc. they should remediate the problem or you can leave a few traps, poison, close holes, etc. as a courtesy.If the problem is very severe, hire a professional and bill back to your tenant if they are unwilling to cooperate. 

Of course they are unwilling to waive the pre-payment penalty because “it’s in the contract”.  

If the team members are unwilling or unable to provide the necessary information, the developer must find alternative resources or seek out new team members who can furnish the required data.

I have had to answer the infamous late night roof leaking phone calls, and dealt with: leaking toilets, leaking water mains, faulty electrical panels, broken water heaters, broken furnaces, underground oil tanks, troublesome septic systems, late rents, tenants dog eating the walls, unresponsive tenants and every other real or imagined rental horror story that people who are either too afraid or unwilling to, use as an excuse not to invest.

Also both ODC and Disrupt Equity both brag on their websites that they manage nearly 1 billion dollars of real estate but are unwilling to fork in the 3 million needed on this Sunbelt fund to keep these deals afloat?