The Simple Situation in Which Two Parties Come Together and Freely

The simple situation in which two parties come together and freely agree to an exchange is ethically legitimate only prima facie because:

A) investigation proves that a simple exchange does not involve unethical situations.
B) a simple exchange involves the consent of both parties involved, which leaves no room for unethical acts.
C) certain conditions must be met before it can be concluded that autonomy has been respected and mutual benefit has been achieved.
D) exchange occurs on mutual consent and for mutual benefit, parties get involved in an exchange only if they see their benefit.