If you want, you can refinance the property at that point to a loan with a longer amortization period. and pull out your initial cash investment (and then some), so your ROI becomes infinite, because you are getting monthly cash with no money invested.

The truth is, there are an infinite number of ways to structure these things.

The $10,000 sitting on your HELOC has a potential future interest cost of $0 - infinite dollars, depending on when you pay the principal.

Forced appreciation, cash out refi, infinite returns.

If you aren't legit and don't have proper licensing and insurance there are infinite situations which could put you and your friend in a bad spot legally or even put your own personal assets in jeopardy on top of being fined for managing a rental without a license. 

I paint all my rentals myself and the paint is only $25 a gallon, it takes me a day to paint an entire unit so for an investment of say $50 plus supplies, I make an infinite return on that improvement.

When demand is infinite you can deal with existential philosophy and sell snake oil over and over again.That is not the case in 95% of the RE market.  

But, I ultimately still made (a little bit of) money on the deal.And I can promise I learned an infinite amount more on that first deal than ANYONE learns in ANY training.

i think you'll be hard pressed to find a 20% COCR with a <$200k property that you're doing LTRs on. unless your BRRR it. then your COCR is infinite. so a better question might be, where can you BRRR with <$200k?

It likely is the effort of a large BRRRR but with a good brrrr I can achieve infinite return at the refi.