Other than that, it works as a cash flowing property with decent returns.  

I have been told it is considered so bad, return of commission is on the table.

If you are a developer that has 10 projects and you make millions each time on 7 of them but the other 3 fail upfront and you lost hundreds of thousands per deal likely still making great return overall.If you are smaller developer with 1 or 2 projects that can really eat into your net worth burning upfront cash on a project seeing if it will take off or not.You could 1031 as mentioned and just buy something yourself.

Lets say you invest the 40k into your duplex and it allows you to raise your rents by $150 per side yielding you another $300 per month and $3600 per year.3600/40000=.09Is a 9% return within your goals?

I then moved to Puerto Rico for 4 years, from there I moved to Texas before returning to Washington.I recently bought a 4(5) bedroom house on 4, 5 are lots in Anacortes, with 2 other people.

I am now a retail real estate agent (and I privately manage SFRs for owners), the trustee sales are almost over for the mid sized flippers around here ("my" money is buying non-performing loans, better returns on time and money). 

The only ones enjoyed better returns are the people who bought at 2009-2011 with cash or high down.

They were happy to put their money to work making a good return. 

The difference is there is zero risk to paying off debt faster, you know your exact return.

That new vehicle is likely to be a passive, LP position with a very strong sponsor / operator relationship I have where his money could be pulled out or reinvested after 24 months and would achieve roughly a 10% cash on cash return payable in quarterly distributions.