How does a county assessor evaluate a duplex

[Luis Gonzalez]

Hi Everyone,

     I am hoping someone here in Oklahoma can help me with this. I've got a seller wanting to sell his duplex. I am working on analyzing the value and to see if its worth it. I'm looking at the county assessor to see what they value the place at and it is way lower than what the seller is wanting. I'm curious, does the assessor evaluates it as per side or does it look at the property as a whole?

Thanks in advance for any help you guys can provide.