Maybe there's an angle for seller financing or some other creative approach to get the seller the total return they want over time, but it's hard to say without actual facts and data.

I previously owned a long-term rental that I bought from a parent and rented to family for over three years (lesson learned!).

 Which city in the United States has appreciated the most over the past 10 years?

I've sold, owned and renovated plenty of plexes over the years and would be happy to chat if you'd like. 

Over time I have amassed a good quantity of houses with no mortgages.

The motivation is not necessarily to scale into larger opportunities but rather to achieve better balance and also optimize the performance of the projects and types of projects I currently pursue.I have no shortage of individuals who possess specific skill set who would want exclusive rights to that particular service vertical in return for contributing capital and a partnership interest (construction background and wants to take over all construction duties or someone who is a sales broker and wants to list all of the properties etc.)

my property appreciation varies from a low of $2700/month to over $10k/month.   

Unfortunately, over the 11 months he has lived there, he has only managed to pay the rent on time once.

In contrast, partial note investors invest in a portion of the loan’s yield, with no single investor holding a priority position over others.

Of course, if we have another available unit that's similar to the one they were looking at, I'll pivot to that and offer to move their current application over to that unit as long as they would still qualify under whatever the new unit's rent is.