> We were able to prove that we could make the financials work so long as we were able to fill the apartment within around 45 days of taking it over.

They're prescreening apartments/leases so they're not going to take on an apartment they can't turn around in a month. And honestly, modeling NYC rental supply and demand according to a number of factors (neighborhood, price, condition, amenities, etc.) is pretty straightforward. It's a relatively liquid market.

And like I said, landlords generally have explicit rules about tenant qualifications. They're not going to reject tenants on a whim. Why would they ever say no to a qualified tenant? That's like McDonald's refusing to sell you a quarter pounder.

There's nothing about this that seems obviously unsustainable at all.

I agree with the rest of your comment, but in my experience landlords in hot markets can be pretty capricious. If they know they'll have a steady stream of applicants, many will definitely reject qualified tenants based on personal whims or to hold out for someone they see as "more" qualified or more likely to stay long term. That said, as long as the apartment still gets turned around quickly then it's not really a threat to this business model.

So a better way to phrase the question would be "Why would they ever say no to all qualified prospective tenants?"

Yes they'll sometimes pick the most qualified applicant, but only if you submit your application the same day or same weekend, which is often the case with open houses. It really depends on the landlord however -- for a lot, it's literally the first qualified person to apply, which is why you want to be the first person to the open house and have all your documents ready to apply on the spot, since it might be gone 30 minutes later.