Is there any case law supporting a claim that defendants breached their duty of care by hiring Valdez?

To the extent that plaintiffs are suggesting that defendants breached their duty of care simply by hiring Valdez, the argument fails. In Torres v. Reardon (1992) 3 Cal.App.4th 831, 841, the court rejected an argument that homeowners caused injuries the plaintiff sustained in a fall by not "assuring themselves that he was competent to undertake the task": Torres had represented to the homeowners "that he was experienced in tree trimming and that he was capable of the undertaking."