Type of postage should be the choice of seller based on value of item and how quickly delivery is required. It is for the protection of seller that cover needs to be adequate.
If a buyer requests that seller uses a method not offered then seller on payment of extra postage should be able to do this.
I cannot think ebay can prevent using what is required if buyer is prepared to pay more, and if ebay cannot provide the service, buy direct at Post Office. Most ebay schemes become too inflexible and best avoided.
