The property tax in Arizona is an "ad valorem" tax. Ad valorem means "according to value". The property tax is based on the market value of the property being assessed.
The definition of market value is:
The most probable sale price of a property in terms of money in a competitive and open market, assuming that the buyer and seller are acting prudently and knowledgeably, allowing for sufficient time for the sale, and assuming that the transaction is not affected by undue pressures." Implicit in this definition is the consummation of a sale as of a specific date and time, and the assumption that financing if any, is on terms generally available anywhere in the community at that place and time.