In San Francisco, renting illegal units is a double whammy as you technically cannot receive any compensation for an illegal space while at the same time you are unable to evict anyone due to the eviction control in San Francisco.

I've had a few clients permit unpermitted units and it cost about double what they expected. 

In North Carolina, you can assign a contract to another buyer without needing to double close... 

I just had a deal that I was helping @Monica Pope with here in Clevleand fall apart because it was a triple that was a legal double.

then ( at least in Oregon) contractor would sue lot owner for unjust enrichment.. and lot owner ends up paying double for many of the trades..

You have a de minimis exception which is set at $2,500, and it can be doubled to $5,000 if you follow certain strict and tedious accounting practices known as AFS.

I do that with a Vegas prop and we get basically double the rent and its A class so no need for PM. 

We learned the importance of thoroughly vetting our title companies and double-checking every detail.

You can then prove your income not get double taxed on passthrough income.

My Class A home (nice suburb with great schools) is doing well but I bought it in 2013 and it has doubled in value from 2013 to 2021.