What must occur for an exchange between a buyer and seller to be considered legal?

For an exchange between a buyer and seller to be considered legal, it is essential that both parties reach an agreement. This mutual consent ensures that both the buyer and the seller are willingly participating in the transaction, which is a fundamental principle of contract law. Without the agreement of both parties, the transaction lacks the necessary foundation to be upheld legally.

This mutual consent involves a clear understanding of the terms and conditions of the exchange, including the price, the items or services being traded, and any other relevant stipulations. When both the buyer and seller agree to these terms, they create a binding contract that can be enforced legally.

In contrast, the other options suggest that consent from only one party or governmental approval is sufficient for a legal exchange, which does not align with the fundamental principles of contract law that require mutual agreement for a transaction to be valid and enforceable.