“An action for money had and received can be maintained whenever one man has received or obtained the possession of the money of another, which he ought in equity and good conscience to pay over. This proposition is elementary. There need be no privity between the parties, or any promise to pay, other than that which results or is implied from one man’s having another’s money, which he has no right conscientiously to retain. In such case the equitable principle upon which the action is founded implies the contract and the promise. When the fact is proved that he has the money, if he cannot show a legal or equitable ground for retaining it the law creates the privity and the promise. 2 Chitty, Cont. 899 (11th Am. Ed.); Mason v. Waite, 17 Mass. 560; Hall v. Marston (17 Mass. 575) Id. 574; Knapp v. Hobbs, 50 N. H. 476; Eagle Bank v. Smith, 5 Conn. 71 (13 Am. Dec. 37). It is not necessary that the defendant should have accepted the money under an agreement to hold it for the benefit of the plaintiff, or that the party from whom he received it intended it for the plaintiff’s benefit. Neither is it necessary that the money received by the defendant should have been an exact and specific sum, belonging exclusively to plaintiff, and entirely separate and distinct from any other moneys. We have found no case which lays down any such narrow rule. Allanson v. Atkinson, 1 M. & S. 583; Heartt v. Chipman, 2 Aiken [Vt.] 162.”
Kondas v. Washoe County Bank, 51 Nev. 134, 271 P.2 465, 466 (Nev. 1928).
Actions to recover taxes paid are equitable in nature, and the burden of proof is on the taxpayer to show that the taxing body holds money that in equity and good conscience it has no right to retain. El Tejon Cattle Co. v. County of San Diego, 252 Cal.App.2d 449, 60 Cal.Rptr. 586, 595 (Ct.App.1967); Hawes v. Smith, 120 Ga.App. 158, 169 S.E.2d 823, 824 (Ga.App.1969). “Such would be accomplished by establishing the plaintiff’s right to the money and the defendant’s possession.” 169 S.E.2d at 824 (emphasis in original). See Estate of Kasishke v. Oklahoma Tax Comm’n, 541 P.2d 848, 852 (Okl.1975) (a claim for refund is one for money had and received, and taxpayer must establish that he has in fact overpaid his tax to recover).
[ State v. Obexer & Son, Inc., 99 Nev. 233, 237, 660 P.2d 981, 984 (Nev. 1983).]
As to the application of such principles in an appropriate case no doubt exists. While certain equity principles are involved, this is not an equity case, but a suit at law for money had and received.
 It is a well-established rule of law, subject to certain qualifications not material here, that money paid in excess of the amount due through a mutual mistake of fact may be recovered. 30 Cyc. 1316.
The general rule was stated by this court at a very early date in Travis v. Epstein et al., 1 Nev. 116.
Mr. Williston in his excellent work on Contracts at volume 3, § 1574, states the rule in the following language:
“One who by error in computation, or by mistake of any fact, pays a real or supposed creditor more than is his due, or pays a debt previously discharged, may recover the overpayment; and generally speaking, money paid over under a mutual mistake of an essential fact, or under a unilateral mistake as to such a fact where the defendant has parted with nothing and the plaintiff has not received an expected return, may be recovered.”
Smart v. Valencia, 50 Nev. 359, 261 P. 655 (Nev. 1927).