Please take special care when shipping any ephemera.
Ensure that any paper or card that you send through the post is secured to a backing board to prevent it getting bent in transit.
Most of all ensure that the emphemera is wrapped in waterproof material to prevent it getting wet in transit.
Ensure that the envelope is strong and reinforce the edges with tape in case they rip.
Remember that the seller is responsible for the item until the buyer receives it, so it is in the best interest of the seller to ensure that the ephemera is wrapped as good as it can be.
Never ever simply throw loose cards or paper into an envelope and mail it - this will damage the ephemera and will usually cause the envelope to rip in transit - if the goods are lost or damaged it is then the seller's fault and not the responsibility of the courier.