EXTREMELY OVER SIMPLIFIED.Just to be clear that is rapid progress for someone in your shoes.

As far a rents go I'd say that is high for the area but rents are going up rapidly here.

Did your lender try to do rapid scoring? 

This area of Harlem is right by the top of Central Park, 2 separate subway stops, and is gentrifying rapidly. 

I just bought a rental in Grand Rapids (3 hours west of Detroit) earlier this year and I'm easily getting a 30% cash-on-cash return.

First, if market values fall relatively rapidly AND you have to refinance the debt (because you have a balloon note, for example), then you can be in trouble if you multiply this issue across many properties.

If you're anticipating a rapidly rising market this isn't a big deal (bank will get a new appraisal).

Houses and apartments will fill-up rapidly.

In the Brewerytown section at least, we're renting to mostly grad students and young professionals in a rapidly changing area of Philadelphia.

Population is growing rapidly due to a lot of companies relocating here.