When, like in this case, only one inference can be drawn from the facts in Minnesota, waiver becomes a legal question. Meagher v. Kavli (In re Meagher), 251 Minn. 477, 88 N.W.2d 871, 874 (1958). A federal court is bound by decisions of the highest state court when deciding a question of substantive law.

An account stated is created if a debtor retains a detailed billing statement without objection for an unreasonably long time. Meagher v. Kavli, 251 Minn. 477, 487, 88 N.W.2d 871, 879 (1958). The debtor's retention of the statement without objection constitutes a manifestation of assent and implies a promise to pay the balance that is said to be owed.

"An account stated comes into being through an acknowledgment or an acquiescence in the existing condition of liability between the parties." Meagher v. Kavli, 251 Minn. 477, 487, 88 N.W.2d 871, 879 (1958). The supreme court summarized the claim as follows:

In Minnesota "`[i]t has long been recognized that substantive law is that part of law which creates, defines, and regulates rights, as opposed to "adjective or remedial" law, which prescribes method [sic] of enforcing the rights or obtaining redress for their invasion.'" Zaretsky v. Molecular Biosystems, Inc., 464 N.W.2d 546, 548 (Minn.Ct.App. 1990) (quoting Meagher v. Kavli, 251 Minn. 477, 88 N.W.2d 871, 879-80 (1958)). Nebraska's statute of repose, at least as it applies to cases like this one in which the injury-causing accident does not occur until after the ten-year repose period has expired, and Minnesota's useful life statute are relatively easy to classify under this test, and we hold that they are substantive law.

[i]n Minnesota, "`[i]t has long been recognized that substantive law is that part of law which creates, defines, and regulates rights, as opposed to "adjective or remedial" law, which prescribes method [sic] of enforcing the rights or obtaining redress for their invasion.'" Zaretsky v. Molecular Biosystems, Inc., 464 N.W.2d 546, 548 (Minn.Ct.App. 1990) (quoting Meagher v. Kavli, 251 Minn. 477, 88 N.W.2d 871, 879-80 (1958)).Id.

We noted that, while a court “will not penalize a client for an exercise of the right” to terminate a representation agreement and settle a matter without the attorney's “consultation or consent,” when the client does so the “measure of relief of the attorney is the reasonable value of his services.” Id. at 285, 176 N.W. at 990; see also Meagher v. Kavli, 251 Minn. 477, 491–92, 88 N.W.2d 871, 881–82 (1958) (stating that when a representation agreement is ended, the attorney is left “in a position where he may only recover the reasonable value of the services he has rendered” and thus “[a]n attorney may recover for his services under a common count in general assumpsit”). This implied term is premised upon the understanding of the parties that the attorney rendered services with the expectation of payment, the client was aware of that expectation, and the client accepted the attorney's services without objection.

However, this court has also observed that, while the freedom to contract between attorney and client is unimpaired, agreements made after services have been rendered should be closely scrutinized to see that there has been no overreaching and that the client was fully informed. Meagher v. Kavli, 251 Minn. 477, 88 N.W.2d 871 (1958); Beals v. Wagener, 47 Minn. 489, 50 N.W. 535 (1891). Defendants urge upon this court the higher standard that an attorney must first prove the contract was fair and reasonable, citing Cooper v. Conklin, 197 App. Div. 205, 189 N.Y. S. 552 (1921).

Retention of a statement of account without objection for an unreasonable time manifests assent permitting "the legal inference that an account stated has been established." Meagher v. Kavli, 88 N.W.2d 871, 879 (Minn. 1958); see also Am. Druggists Ins., 349 N.W.2d at 573. Once shown, an account stated is only prima facie evidence as to accuracy of the account and the liability of the debtor; such a showing may be overcome by clear and convincing evidence of fraud or mistake.

Waiver is the voluntary relinquishment of a known right, which can be inferred from a party's conduct. Meagher v. Kavli, 251 Minn. 477, 486, 88 N.W.2d 871, 878–79 (1958). Similarly, under the doctrine of account stated, if one party renders a statement of account to the other party, and that other party retains the accounting for an unreasonably long time without objecting to it, then the party is deemed to have assented to that accounting.

Waiver is the voluntary relinquishment of a known right, which can be inferred from a party's conduct. Meagher v. Kavli, 251 Minn. 477, 486, 88 N.W.2d 871, 878–79 (1958). Similarly, under the doctrine of account stated, if one party renders a statement of account to the other party, and that other party retains the accounting for an unreasonably long time without objecting to it, then the party is deemed to have assented to that accounting.