Square footage Discrepancy

[Kainoa Jones]

Hello,

There is a potential property I am looking into with differing tax assessor and appraisal/ MLS sqft. There was an addition to the property prior to the current owner and my guess would be that the addition was not permitted. In Washington state, how can this discrepancy be fixed? Also, how much does this usually cost? The last thing I would want would be to incur back taxes.

Thanks!