Start with the statutory valuation date
King County values property for a specific January 1 valuation date. A purchase close to that date usually says more about market value than a transaction separated by a long period of market movement or major physical change.
Write the sale date, contract date, closing price, county value, and valuation date on one timeline. Then identify credible market evidence showing whether prices changed between those points.
Show that the sale reflects the market
Explain how the property was exposed to the market, whether buyer and seller were unrelated, and whether either party faced unusual pressure. Preserve the listing history, purchase agreement, settlement statement, inspection, and appraisal if they help explain the transaction.
A family transfer, foreclosure, bundled transaction, substantial seller concession, personal-property allocation, or unusual financing may require more explanation. These facts do not automatically erase a sale, but the Board needs to understand what the price represents.
Reconcile the sale with property changes and other evidence
List remodeling, repairs, damage, demolition, permits, or occupancy changes between the valuation date and purchase. A price for a home needing major work is not directly comparable to the same home after renovation.
Add a small set of relevant third-party sales. When the subject sale and comparable sales point to a similar range, the requested value is easier to defend. If they conflict, investigate why rather than selecting only the favorable number.
File around one supported value
Do not assume the Board must adopt the purchase price. State the value supported as of January 1 and connect the subject sale, other sales, market movement, condition, and transaction terms to that figure.
Protect the ordinary July 1 or 60-days-after-mailing deadline while gathering documents. Confirm the parcel-specific date in eAppeals and retain the submission confirmation.