A quick formula you can use is your estimated purchase price times .0134. 

Purchase price: $255,000 Cash invested: $100,000 Single family residential home in A Class neighborhood.

I purchased a house a couple of years ago and a portion of the purchase price was done with seller financing. 

It makes the math very tough on purchasing, at least from my perspective. 

Purchase price: $171,000 Sale price: $185,000 Contributors: Peter Vekselman Partner Driven teamed up with Nathan Ward to secure a profitable deal on Day Rd in Leoma, TN.

Find deals and use the private money to purchase  and flip them.

Purchase price: $40,000 Cash invested: $65,000 Purchased this 2 bedroom, 2 bath mobile home on a 2 acre lot with well and septic.

This amounts to lost opportunity because if you had purchased RE, at the closing it can start producing return. 5) ADUs detract from the existing structure whether this is privacy, a garage, or just yard space. 6) this is related to number 1, but there are many more buyers looking to purchase homes for their family than there are RE investors looking to purchase small unit count properties.

As you alluded to, sometimes a passive note investment purchased for monthly payments “goes south”, and becomes an active participation investment, with plenty of additional capital required for legal fees, forced place insurance, and property taxes.  

Purchase price: $300,000 Cash invested: $50,000 Purchased a 12 unit park owned mobile home park on a 5 acres.