Considering purchasing property, but current rent is far too low

[Nicole Cotrino]

We are currently considering a rental property in Bend, Oregon, but the current rent is far too low. It is a duplex with a list price of $332,000. Current rent is $800 per unit. It's in a great neighborhood, in good condition, and the area has an extremely low vacancy rate (less than 1%). All the research I have done (including Rentometer, Zilpy, talking to my realtor, and contacting a property manager in the area about it) has put the fair market value at $1200 per unit or more (so total income of $2400). 

As a new investor, I'm just curious what other people's experiences have been in situations like this. If I base my calculations off an income of $2400 and make a low offer, the numbers make sense to me. But, if I use $1600 total, the numbers don't make sense at all. 

Thanks in advance!