700 sqft Difference Between Assessor Records and Reality - How to Fix??

[Brandon Foken]

I'm working with a seller who owns a house with a significant square footage difference between county records and the actual size of their house. County records show it's a 3/2.5 with 2,323 sqft. In reality, the house is a 3/3 with 3,006 sqft. The seller did an addition back in 1989 and has the full permit history associated with the construction. I gave the seller an offer based upon county records, but they now want me to give a revised offer based upon their actual size. I've spoken with them and they are fine with a contingency ensuring that I can get county records to accurately reflect the sqft of the house.

So, my question is, how do I go about getting this fixed? I've called the assessor's appraisal office a few times only to be met with their voicemail each time so I'm not getting any help from them. In general, what would the process be to get the square feet accurately reflected + rough timeframe and costs?