Others can correct me if I'm mistaken, but I've been told that the auditor here in Hamilton county generally recognizes arm's-length transactions (such as ones listed on the MLS) to be considered an appropriate valuation of the property.

@Eddie Pietschmann You should obtain lists from the county auditors' website.

I also wanted to note, if you are purchasing the duplex at a price that is significantly below the auditor's appraised value of the property, you can file a complaint and try to get the appraised value lowered.

Personally, I'm not at the point where I'm spending tens of thousands on marketing, so it's not worth it for me to pay for a subscription every month and buy the leads, particularly when you can find this information yourself with some digging as it's all public record (checking the county auditor's page, finding when the mortgage was recorded, pulling your own comps, etc.) 

As the county auditor will see the new sale price.This may be even more of an issue here because of how hot the RE market is.For example:I bought a double last year for 175k.