My wife and I used this on our primary that we later turned into an investment property.

Our form lease forbids any adult from living in the house who is not on the lease, but am I just setting myself up for a fight later?  

He was out 7 days later, new locks and repairs are underway. $850 was equivalent to his rent.

The literally single biggest mistake that people make is to buy a class D property, because it was cheap to begin with, 90+ days on market and they were able to negotiate a "discount" - ask them a year later how that worked out for them. 

Only loan that would cover your rehab is an FHA 203K (primary residence loan) OR hard money fix and flip loan and you would have to refinance later.

I bought my first duplex in 2021 along with a single family home a few weeks later.

This bit me a few months later when I sent direct mail and handwritten letters to homeowners as a wholesaler.

Say you start a STR and use the loophole to write off 100k from W2 salary. 2 yrs later the rental goes underwater and you have to give it up at huge loss.  

Note: if roommates change during the tenancy, a lease addendum is signed and the security deposit is called out so that there will be no confusion in the future, 'The Landlord and the Tenant's agree that . . . '  This lease addendum may also guide your bank record when the funds are withdrawn later.

The fact that article came out in 2001 and that hasn’t happened yet nearly a quarter of a century later literally just proves my point.