When a formal written appraisal is required, the next determination is to the purpose and use of that appraisal. Insurance appraisals have different requirements and can represent different values than estate tax or charitable donation appraisals. Appraisals that will be used for tax purposes require the use of fair market values. The IRS defines fair market value as "the price that property would sell for on the open market. It is the price that would be agreed on between a willing buyer and a willing seller, with neither being required to act, and both having reasonable knowledge of the relevant facts." IRS Regulation §20.2031-1 While fair market value can be determined using the prices realized at auction --- one must take into account any fees associated with the auction sale, such as buyer's premium (as high as 25% at some auction houses --- 15% or 19.5% at Heritage). These additional fees must be considered as part of the sale price --- and thus fair market value.
The IRS also stipulates that "The fair market value of a particular item of property ... is not to be determined by a forced sale price. Nor is the fair market value of an item of property to be determined by the sale price of the item in a market other than that in which such item is most commonly sold to the public, taking into account the location of the item wherever appropriate. Thus, in the case of an item of property ...which is generally obtained by the public in the retail market, the fair market value of such an item of property is the price at which the item or a comparable item would be sold at retail." 26 C.F.R. §20.2031-1(b) A qualified appraiser should look at the proper and true market for a piece of property to determine how best to establish the fair market value --- whether that be at auction or in a retail environment.