Wash. Rev. Code § 51.52.102
At the time and place fixed for hearing each party shall present all his or her evidence with respect to the issues raised in the notice of appeal, and if any party fails so to do, the board may determine the issues upon such evidence as may be presented to it at said hearing, or if an appealing party who has the burden of going forward with the evidence fails to present any evidence, the board may dismiss the appeal: PROVIDED, That for good cause shown in the record to prevent hardship, the board may grant continuances upon application of any party, but such continuances, when granted, shall be to a time and place certain within the county where the initial hearing was held unless it shall appear that a continuance elsewhere is required in justice to interested parties: AND PROVIDED FURTHER, That the board may continue hearings on its own motion to secure in an impartial manner such evidence, in addition to that presented by the parties, as the board, in its opinion, deems necessary to decide the appeal fairly and equitably, but such additional evidence shall be received subject to any objection as to its admissibility, and, if admitted in evidence all parties shall be given full opportunity for cross-examination and to present rebuttal evidence.
RCW 51.52.102