Your SFHome or apartment isn't zoned for business,, if they have anyone coming to residence for that purpose,, hair cutting, tattoos, tax work,massage parlor, drugs, or daycare,,,,,, its gonna be a issue..  

You know better, even if it's just a hinky feeling that you have that brings up the hairs on the back of your neck.Once you take money from this tenant, you owe them.  

I’m talking about elderly people whom make money from their barber shop, hair salon or maybe from selling sport equipment out their shop that they need to pay rent for.

I'm looking up at one right now and really, really, don't feel like getting out a ladder and ending up with a ton of dust in my hair and all over my living room....sigh. 

It depends on some major factors that have already been covered: class of the building/area, payment and behavior history of the tenants, how much works needs done to the units if they are vacated, how much you can increase the rents for new tenants, how quickly the units will rent/how hot the rental market is in that area, how much you do or don't mind having to find and place new tenants.Sometimes I'll get a multifamily with GREAT tenants in them that are paying market rent, or maybe just a hair below, and they've maintained the place very well.

My only problem has been a commercial space where a hair salon had to shut down due to covid and I let them out of the lease. 

For instance, what if you had a fee that said that people with brown hair had to pay an extra fee. 

In terms of legitimate numbers, besides the construction cost above, remember that the majority of these homes are very old and adding rooms can be tedious, stressful, and might make you want to pull your hair out!

Also, be sure to have multiple car dash cams, and ring cameras in every room.Don't ever go in the same room alone, never close the front door or any door in the house, never look her in eye, for goodness sake never make any comments about her clothers, hair, appearance......depending on what specific things listed above, you think are a joke or good common sense, will determine your level of neuroticism about the topic and should probably let you know if you have right mind set for the leasing agent job...jus sayin

I know its splitting hairs and probably wont matter, so I'm just wondering.Thank youJohn