In Carleton v. Tortosa (1993) 14 Cal.App.4th 745, the client sued the broker, alleging negligence because the broker did not advise the investor that his transactions could have adverse tax consequences and by not structuring the transactions as tax-deferred exchanges. The court noted that, although "the degree of care and skill required to fulfill a professional duty ordinarily is a question of fact and may require testimony by professionals in the field if the matter is within the knowledge of experts only. . . . Expert testimony is incompetent on the predicate question whether the duty exists because this is a question of law for the court alone." (Id. at pp. 754-755.) The Carleton court, rejecting the claim that the expert testimony showed the broker had the duty to create contractual language insuring the transaction would qualify as a tax-deferred exchange, reasoned that: "Brokers are subject to two sets of duties: those imposed by regulatory statutes, and those arising from the general law of agency. Plaintiff does not contend defendant failed to fulfill a duty imposed by statute or implementing regulation . Thus, he must derive defendant's duty from the general law of agency, i.e., from the agreement between the principal and agent. 'The existence and extent of the duties of the agent to the principal are determined by the terms of the agreement between the parties, interpreted in light of the circumstances under which it is made . . . .' " (Ibid.) Carleton then examined the contractual agreements and noted that the documents repeatedly cautioned the client that defendant broker was "qualified to advise on real estate," but that plaintiff should "consult an appropriate professional" for legal or tax advice. These clauses, concluded Carleton, negated the client's claim that the broker had the duty either to advise him on the legal rights created by the transaction or to prepare documents and structure the transaction to achieve a tax-deferred exchange. (Id. at pp. 755-757.)