Confused or Worried about rental rates, am I missing something?

[Jonathan Davis]

I am interested in a duplex that is in my local area. I have ran the numbers through the BiggerPockets calculator and the rental rates will not let the numbers work. Using the property insights under tools it shows that the rental rates are 100 less than they need to be to make the property work for me, and by the way the property comes with an extra lot that another duplex could be added.  This may just be a fear factor for me and all I have to do is raise the rate when lease agreements expire. My question is how reliable have you found the rental rate insights to be?