What i do is regular envelope but i will have it in a soft plastic sleeve and wrapped.in newspaper with do not machine and do not bend on the envelope. Shipping is more expensive if using bubble wrap envelope and if listing many cards can get expensive but if buyer is willing to pay the shipping for the bubble wrap envelope then i am willing.
Ill explain my feed back ive sold in total 5 cards 3 are sent waiting for feeback other 2i listed had complications with the buyer due to him being bossy and agressive and hostile towards me so i explained to him id refund credits to him cause i didnt feel safe sending my address to him.