He did not include expenses for insurance, property damage, paying tax and so on. And he still was only able to turn out a healthy profit in one of four locations.

Does not look like a viable business idea to me.

However it may be a good way to lower rent or afford an oversized appartment.

Essentially, he's operating as a realtor, or landlord-as-a service. A broker, a middleman, who smooths the process and reassures customers. It doesn't seem very scalable, but if it doesn't take much time then great.

Let me ask the question everyone else is - when will I have the time to do this? Haha.

Then one of your guests brings bedbugs and the nightmare begins.

Or accidentally causes a fire which damages the building and the other tenants property. His insurance would definitely not cover anything like that.