The principal of account stated, "an agreement between parties to an account based upon prior transactions between them with respect to the correctness of the account items and the balance due. By retaining billing statements and failing to object to the account within a reasonable time,  the recipient of the bill implies that he or she agrees with the sender regarding the amount owed."  is a powerful, and often determinative Issue.  In Brunelle & Hadjikow, P.C. v O’Callaghan 2013 NY Slip Op 31302(U) June 17, 2013  Sup Ct, NY County Docket Number: 158213/2012 Judge: Shirley Werner Kornreich it is the decisive and only factor considered.

"There is no doubt that B&H is entitled to an account stated on all amounts included in the June 7 Bill. O’Callaghan’s written acknowledgment that he owed those amounts precludes his current objections as to how they were calculated, such as his qualms about rate increases. As for  O’Callaghan’s objections to the amounts billed after June 7, 2006, which were made for the first time in his December 27,2006 letter, he is precluded from objecting to virtually all of the amounts billed because his objections were not made within 30 days of the relevant monthly invoices (except for his objections to invoices sent after November 27,2006). Nonetheless, even if he were entitled to challenge all of the invoices sent after the June 7 Bill, his objections would still fail. First, his objection to the rate increases, provided for in the Retainer, occurred long after such increases went into effect and were billed. Second, his objection to being overcharged for the NYSE appeal fails because the invoices clearly evidence the credits that lowered the appeal billings to $75,000. His self-serving contention about B&H billing him more than $75,000 for work on the appeal (they purportedly billed it as work for his other NYSE proceedings) is refuted by the invoices and is  insufficient to defeat summary judgment."