Duplex rents vs apartment rents

[Leigh Ann Smith]

We are looking at a duplex for a buy and hold  that is across the street from an apartment complex where comparable units to the duplex are $1200/month.  However, when I checked potential rent for the duplex on Rentometer, it said $800-$900/month.  There are about 10 duplexes on this street, but our realtor did not find any rental comps for duplexes.  Any general rule about duplex rents?  Should there be some reason they'd rent for less  than the apartments? We would plan to do a decent rehab and update.