A.R.S. § 42-18125

If by mistake or wrongful act of the county treasurer, recorder or assessor, or as a result of double assessment, a real property tax lien is sold on property on which no tax is due, the county treasurer shall hold the purchaser harmless by paying the purchaser the amount of the principal and interest at the rate bid and endorsed on the certificate of purchase or ten per cent per year simple, whichever is less.