We see people package things in a number of ways. We like to keep it simple. Most trading cards can simply be placed in a weather proof bubble mailer or rigid cardboard mailer. Place those cards with a sleeve in a sturdy top loader then use painter's tape at the top so the card doesn't slide out. Do not use regular tape as that is overly sticky. Then wrap it in a team bag so if there is any type of water intrusion to the outside package you have a little more protection. We have seen many people use rectangle cardboard cuts and tape them to the top side and bottom side of the top loaders for even more protection.

One thing we will say is that we tend to find that a lot of sellers over-package their items and it makes it hard for buyers just to get in. We have actually damaged our own cards by opening packages that were overly complicated to get into. We guess it is best to be safe, however, when it takes us 20 minutes to cut through a full ball of tape it gets a tad frustrating.