There is an instruction page for packaking cards published by cardmarket. It involves taping and protection postacrds. Usually cards are low value and I have not wated spend much time in packaking.

Ihave come up with a way to secure the card easily and fast.

I use thick paper and cut it four times. Once for each corner of the card. This way it cannot slide out of the sleeve and does not move in side the envelope. Also the face of the catd is protected.

This kind of card holders could be manufactured by a printing shop and it could be in some brand colors.