There's a reason that informed consent is required for medical procedures, even lifesaving ones.
Informed consent is the process in which a health care provider educates a patient about the risks, benefits, and alternatives of a given procedure or intervention. The patient must be competent to make a voluntary decision about whether to undergo the procedure or intervention. Informed consent is both an ethical and legal obligation of medical practitioners in the US and originates from the patient's right to direct what happens to their body.
I know that it's a stretch to apply medical ethics to business deals but I believe the principle of informed consent is still a moral requirement. An example of how this is the intent in many legal systems is the concept of a "meeting of the minds" being a mandatory part any legally valid contract. "Meeting of the minds" is similar to the idea of informed consent:
This was a violation of Yishan’s fiduciary duty to Condé Nast. It’s illegal.