The Statutory Open Market: Case Law - the Vendor
It was established at a very early stage in the development of the case law on valuation that the hypothetical vendor was anonymous. This ensured that the taxpayer could not say in argument (for instance) “I would not have sold at that price”: see IRC v Clay  3 KB 466, at 473.
In Re Crossman [House of Lords]  AC 26 Lord Blanesburgh said:
“If the duty of the Commissioners is, as I think, to estimate the price which the “property” as at the time of the deceased’s death would fetch in the open market, if it were to be offered for sale, it is unnecessary to inquire by whom the property would hypothetically have to be offered.”
In re Lynall CA  3 WLR 984:
“Of course, the hypothetical vendor may be a director, but he equally well may not be a director. One must, therefore, only endow him with the characteristic which must necessarily belong to all hypothetical vendors, namely, that of owning the block of shares in question. “
Cross L J at page 995
The seller (as well as the buyer) is “willing”:
“I think a willing seller means one who is prepared to sell, provided a fair price is obtained under all the circumstances of the case. I do not think it means only a seller who is prepared to sell at any price and on any terms, and who is actually at the time wishing to sell. In other words, I do not think it means an anxious seller.”
(Clay at 478).
Also in Lynall as above
“It is true that the so called willing vendor is a person who must sell: he cannot simply call off the sale if he does not like the price….”
Harman L J at page 986
(Shares and Assets Valuation (SAV) does not accept that this means a forced sale, but only that the sale must take place for the purposes of the statutory hypothesis, and it cannot be called off simply because one party cannot get his price.)