In fact, I'd argue that it is actually the most challenging form of "real estate investing" out there (and I've done it all.. wholesaling, house flipping, ground up development, office, medical, short term rentals, long term rentals)My 2 cents is that you mentor your son to become a rock star realtor.

We have a fairly decent size buyers list and network and previously, have had nearly no trouble selling our deals.There has not been a drastic change in the quality of our deals (of course the nature of the beast allows for the occasional seller who wants too much for their property or the crazy rehab/tear down situation but speaking generally) and I would argue our buyers list has grown significantly. 

The tenant who was arguing with me lived there 20 years whereas my mother has only been there for a few years.

Some may argue that we are currently in a recession.

It is why I would argue for hyper conservative numbers especially on the revenue side in almost all markets. 

They argued that since that new tenant signs the lease, it doesn't matters when he moves in as the lease, in theory, would continues.Who is right on this? 

Maybe, but less likely than wanting ABC Realty Group. 

Xyz for her Abc, and it interrupts your medical practice day, before it become "too much" of an "Interruption.Because my guess is the Medical practice will not be allowed to suffer, nor will the practitioner (for very long).I'm not saying don't do this, what I am saying is try to get comfortable with the amount of time you will have to "give up" somewhere else to get this tax savings.I don't do AirBnB, but it might be intelligent to try to figure out ahead of time how much time this will take YOU, to get set up, and to handle on an ongoing basis.A significant other who is onboard with time commitment and chores involved might make this a no brainier too.Good Luck!

The REI company (ABC) would be independent of her consulting company and I would be running ABC.

And there are plenty of tenant-friendly attorneys who would take this case, argue it in court, and probably win.