The position of an expert valuer carrying out a determination in accordance with the requirements of a contract between two other parties is very different from that of a trustee exercising an unfettered discretion under at trust instrument such as a will or settlement. There is no warrant for importing into the law of contract a rationale developed in quite a different context in the law of trusts.
True it is that the valuer, as expert, is called upon to exercise skill, judgment and an element of discretion, but he or she must exercise that discretion within the confines of the character of the valuation which the parties to the contract have stipulated will bind them.
The valuer's discretion does not permit a refusal to take into account the matters which the contract directs be taken into account, nor does it permit a valuation upon a basis different from that which the contract requires.
In my opinion, unless the contract clearly provides that the expert valuer's reasons for a determination are unexaminable, then either party to the contract is entitled to call into question whether the determination conforms with the contractual requirements.
That question is not for the valuer to determine in effect, by exercising a discretion not to disclose reasons, thus depriving the parties of a means of ascertaining the matter for themselves.
The contract may entitle the valuer to give only a non-speaking valuation, but that is not the same thing as prohibiting the parties from eliciting, by legal process or otherwise, what the valuer has actually done.