Check Rents First!

To get a good idea of what kind of rent you can get, ignore anything the previous owner tells you and start looking around the neighborhood.  You can either ask around, or start checking the classifieds.  Make sure you know where the comps are located and what they look like, as rents can vary widely based on neighborhood and amenities.  Another useful tool is Rent-o-Meter.  It gives you a Zillow-like estimate of what rents are like in a given neighborhood.  Check it out at www.rentometer.com.