Not a realistic guideline anymore.Conventional financing is approaching DSCR and if you want to factor in hassle vs. no hassle, there is no comparison; DSCR vs Fannie is a no brainer; DSCR all day long.30 year amortization is widely available with rates in the 4's and 5's on a 30 year fixed amortization up to at least 8 units and sometimes 12. 

I have a no pets policy for my rental, a one bedroom apartment that is an ADU on the bottom floor of a larger house that is a separate rental above, because there is less insulation between the walls, and the noise carries and barking could disrupt the other tenants.

Seems like a no brainer.

By the way, this is not a no-money business.

100 hour test is a no go if both of you want to use it.

To the original question, I guess that's a no.

I have mixed feelings about it: they're a no-fuss, hardworking people, but the amount of mud they can bring into the house...

I also have a no windows open clause while heat runs. 

They were able to obtain a free 90 day option from you at a fast close all cash discounted price by leading  you to believe that they themselves were going to be the buyer in a no hassle close, and the language of the contract was explained away as required for showing to one of their imaginary all cash investor-buyers.  

I think it's more than possible, but you have to have a no-nonsense way about it.