It is important to ship cards without causing any damage. Here is how I ship my trading cards to customers.
How to Ship Trading Cards the Right Way
I insert all cards into penny sleeves and use top loaders for extra protection. For orders containing more than two cards, I add cardboard and filler cards to protect the main cards. I then seal the top loader to ensure the cards do not fall out during shipping. While bubble wrap envelopes are optional, they are highly recommended for added security. Regular paper envelopes are usually sufficient as well.
With this packaging method, cards arrive to buyers in the best possible condition. I have shipped over 1,000 orders and have not received a single complaint.