However, the tenant opened the door, and I asked the inspector if he wanted to check inside.

"Removing a door and leaving it open"  are you pulling the door casing, replacing it with drywall, trim board?

Most deals will tout "buying this deal at only $XX,000 per door".  

If Planning does determine the existence of your ground floor unit, it will require you to legalize the unit through the existing Planning code process assuming zoning supports the third unit OR using the new ADU program making your fast track condo conversion a passing dream.With regards, to some of your latter comments and questions:1) Any un-permitted work (including corrections) is not a good idea as a quick compliant from a neighbor can bring an inspector knocking on your door with a NOV especially in the current environment where everyone is SIP.2) Legalizing existing constructed spaces can be hit and miss based on the inspector you get.

This conversation would need drywall + 1 door min (not sure if a closet is also need to qualify as bedroom). 

By qualifying based on the property’s income potential, these loans open the door for both new and experienced investors to grow their portfolios and build wealth through real estate.

Looks like someone would have to knock on doors until they can get 3 people to vouch that the property has been like that since before the zoning laws were in place (in 1976?)

Hey Nikki, I invest in Detroit (12-doors there) and live in California.

A house has come up for sale next door to one of their existing houses, and due to the convenience that would provide from an operational standpoint, they want to open up shop there.  

Yesterday I went to the home to see the condition, there was no car on the driveway… I opened the main door to peep inside…looks like they still have lot of their stuff inside and I can smell bad odor; I just closed the door and returned back.