Market Value is the estimated amount for which a property should exchange on the date of valuation between a willing buyer and a willing seller in an arm's-length transaction after proper marketing wherein the parties had each acted knowledgeably, prudently and without compulsion - definition adopted by the International Valuations Standards Commitee. Price is the amount of money for which something is sold for.
It is important to distinguish between Market Value and Price. A price obtained for a specific property under a specific transaction may or may not represent that property's market value: special considerations may have been present, such as a special relationship between the buyer and the seller, or else the transaction may have been part of a larger set of transactions in which the parties had engaged.
Another possibility is that a special buyer may have been willing to pay a premium over and above the market value, if his subjective valuation of the property (its investment value for him) was higher than the Market Value. An example of this would be the owner of an adjoining property who, by combining his own property with the subject property, could enjoy a higher value for the amalgamated land parcel (i.e. 'the sum is greater than its parts'). When such situations arise in property markets, it is the task of the property valuer to determine whether a specific price obtained under a specific transaction is indicative of Market Value.