Which of the following is a guideline per the Mail or Telephone Order Merchandise Rule of $1993$ in relation to mail$-$order sales?

Multiple Choice

Sellers must ship the items within the promised time.

Sellers should refund $50$ percent of the value in case of cancellation of the mail order due to a delay on the side of the seller.

Sellers must notify and confirm the order through an oral conversation with the customer.

As far as possible, the seller should not give the customer an opportunity to cancel the order.