Duplex comps - Sacramento - anyone knows appraising process?

[Raman Bindlish]

Hi,

I am looking to refinance a duplex in Sacramento that we bought 2 years back and there are hardly any comps available in the neighborhood. 

What are the ways I can estimate the appraisal of the property? Single family houses in the neighborhood have been going up at more than 10% annually since I purchased and I have renovated and raised rents by 40% in 2 years. So, I am hoping that the appraisal comes out at a significant higher value. But when I look at Realtor.com estimate, the duplex shows up as 10% up from our purchase price. 

Even though cap rates do not directly apply to Duplex, what is a typical multi-family cap rate in Sacramento these days? 

Tax assessment is pretty low for the area for some reason and that is a critical factor in realtor.com estimate. I am wondering what appraisers look at in absence of comps of similar units and how they come up with value. Any feedback would be appreciated.

Thanks
Raman