City got their tax money, my seller had a sizable profit, the buyer built a spec house (that went under contract in 7 days) and the neighborhood benefits by the subtraction of a dangerous vacant parcel and the addition of a brand new home!

Title: The Hidden Dangers of Underwater Fix & Flip Projects: The Erosive Power of TimeThere's an escalating situation within the fix & flip domain that we feel needs to be brought to people's attention - underwater projects.Underwater projects occur when the outstanding loan value surpasses the current market value of the property.

Sounds petty, dangerous, and heartless.

Income from STRs is generally considered active income if you’re directly managing the property, which typically subjects it to a 15.3% self-employment tax.To mitigate this liability, strategic entity structuring can be effective.

Also, Detroit is #6 on Neighborhood Scout’s list of the 100 most dangerous cities.

@Jacques Herve things just sound easy and simplistic when talking about stuff but renting rooms is complicated, convoluted and can be dangerous.

And what could one do to mitigate any such effects?

They never received the cards, I keep them, so there’s no danger of them ever using them on anything and they get the benefits of the higher score.  How does having the authorized users affect your own credit score?

But just starting out where you just have one or two is probably the most dangerous time as far as finances go if you aren't deep on cash.  

Of course it can happen but again, caught early, mitigate damage and move forward.