Cal. Rev. & Tax. Code § 1609

The hearing need not be conducted according to technical rules relating to evidence and witnesses. Any relevant evidence may be admitted if it is the sort of evidence on which responsible persons are accustomed to rely in the conduct of serious affairs, regardless of the existence of any common law or statutory rule which might make improper the admission of such evidence over objection in civil actions. The applicant shall have the right to introduce evidence concerning the terms of sales of comparable property that has been sold.