The W-9 isn't the mechanism with which you elect an entity's tax classification. 

So I’m major appliance hunting and I’m finding a lot of the supply of bullet proof mechanical controlled appliances being replaced by electronic controlled appliances.

It will also depend greatly on the building itself and the age of the mechanicals etc...

But the same could be said of an auto mechanic.

For example, I don't think a mechanic's lien will come up in a court search.  

Having the mother cosign is great but I wouldn't put an emphasis on it, she sounds like a risky tenant and unless finding qualified tenants in your market is challenging I would hold off on this one. 

I look hard at the structural soundness and mechanicals of a building.

This was an auto body shop and paint booth for over 20 years and not used for mechanical work much at all. 

The exact mechanics depend on how your business is structured, but there is no "rent" involved either way.

I would have them walk between 6-10 units, common areas, roofs, mechanicals, etc.