If you're planning to rehab properties for rental or flipping, a hard money lender might be the right fit.

My father-in-law told me he plans to sell his 6 unit condo building ASAP so he can "retire" from being a landlord.

I've never taken one and don't plan to, but good to hear from someone that went through it.

The cash on cash return is only meaningful when you evaluate it based on your long term plans.

I have employer sponsored plans that match contributions as well as a solo 401k and I do a backdoor Roth. 

It depends how long you plan on living.

It might be worth a follow-up closer to the move-out date to confirm their plans, but avoid excessive contact to prevent escalation.

@Marcos Carbi  If you want to allow a payment plan, Tell them this is the best I can do:Pay $xxx cash by tonight at 8pm for November's rent. and then beginning Monday Jan 20, pay $450 each Monday (in cash?

We have reported him to several places and plan on continuing to report him to other places. 

You snowball plan has a very high success rate.