A client is free to sue his professional, whether it be an attorney, an accountant or even a doctor.  But, if the client has "dirty hands" or has participated in some untoward act, he may be blocked from pursuing the case.  This is the principal of "in pari delicto."

In an accounting setting, Schwartz v Leaf, Salzman, Manganelli, Pfiel, & Tendler, LLP  2014 NY Slip Op 08823  Decided on December 17, 2014  Appellate Division, Second Department  is an example of the rule and an exception.  Where an agent engages in wrongdoing, that misconduct may be attributed to the principal.  Sometimes not. 

"The Supreme Court properly denied that branch of the defendants’ motion which was to dismiss the accounting malpractice cause of action pursuant to CPLR 3211(a)(1). The defendants contend that that cause of action is barred by the doctrine of in pari delicto, "which mandates that the courts will not intercede to resolve a dispute between two wrongdoers" (Kirschner v KPMG LLP, 15 NY3d 446, 464). However, the adverse interest exception to the doctrine of in pari delicto provides that "when an agent is engaged in a scheme to defraud his principal, either for his own benefit or that of a third person, the presumption that knowledge held by the agent was disclosed to the principal fails because he cannot be presumed to have disclosed that which would expose and defeat his fraudulent purpose" (Center v Hampton Affiliates, 66 NY2d 782, 784). Here, the documentary evidence submitted by the defendants did not conclusively foreclose the application of the adverse interest exception to the in pari delicto defense (see Symbol Tech., Inc. v Deloitte & Touche, LLP, 69 AD3d at 196-199; compare Chaikovska v Ernst & Young, LLP, 78 AD3d 1661, 1662-1664)."