Until I had a look at this judgment, I thought that the best evidence of the value of land at a particular point in time would be what people in the real world actually offered to pay for it. In fact, there seems to be a lot of authority for the proposition that such evidence is inadmissible to prove what the land was worth. The whole question was reviewed in the utmost detail in Auxil Pty Ltd v Terranova  WASCA 163. Justice of Appeal Buss with whom Justice of Appeal Miller agreed kindly summarised the fruits of their review as follows:
46 First, the general rule of admissibility is that an unaccepted offer to
purchase land is not admissible as ‘direct evidence’ of its value.
47 Secondly, the general rule does not exclude evidence of an unaccepted offer in each and every case.
48 Thirdly, where evidence of an unaccepted offer to purchase land is sought to be tendered, the purpose for which the tender is made should be ascertained and analysed.
49 Fourthly, although an unaccepted offer to purchase land is not admissible as ‘direct evidence’ of its value, the evidence may be admissible, in a particular case, for limited or general purposes.
50 Fifthly, the limited or general purposes for which evidence of an unaccepted offer may be admissible include establishing:
(a) that later sales sought to be relied on in assessing the value of the land were not forced sales;
(b) the existence of a person who might be prepared to pay more than the ordinary market value of the land;
(c) the demand in the market for the land in the context of evaluating whether a mortgagee of the land breached its duty of good faith in exercising its power of sale;
(d) the special potentiality of the land for a specific purchaser where the offer has been made by that purchaser and in respect of that land.
Also, an unaccepted offer to purchase land may be admissible for the general purpose of providing some assistance in determining the lower limit of the market value of the land in the case of a purchaser’s actual unconditional open offer to purchase at a specific price or for the limited purpose of checking the methodology adopted by an expert valuer in his or her evidence. The illustrations I have given are not, of course, intended to be exhaustive.
51 Sixthly, evidence of an unaccepted offer to purchase land should not, ordinarily, be accorded any weight unless the trial judge has found that the offer was genuine. Factors to be considered in evaluating the genuineness of an offer include, for example, whether the purchaser was willing and able to complete the purchase in accordance with the terms of the offer, whether the purchaser was at arm’s length from the vendor, and why the
offer was not accepted.