If Alice and Bob buy a house for $100,000, and one of them needs to buy out the other's share soon after, would the fair market value be $100,000 (the purchase price) or $94,000 (what they would get after brokers' fees if they sold it)?
While I understand that prices are generally whatever people can negotiate, assume that Alice and Bob either want to be fair with each other or have a contract requiring one to pay the other the fair market value for their share.