When sending cards: Zero movement!

I recommend also using a top-loader inside of cardboard. Postal carriers will bend envelopes to fit them into mailboxes (whether or not they are marked "do not bend"). The combination of a top-loader and cardboard makes it too much work to bend, while one or the other on its own can fail.

For my store, my shipping method is :

A few cards go into a top-loader, wrapped in plastic wrap (I've also had cases where an envelope or package was left in the rain on a doorstep at delivery, so a little bit of waterproofing is good) which goes into a rigid cardboard photo mailer.

Anything more than 10 cards or so goes into a rigid plastic box, wrapped in plastic wrap, and into a bubble mailer.

I buy all the above in bulk, so for the casual trader the cost may be too much. But if you buy from anyone who's not giving you good protection from careless mail carriers, think of this - at the point that you buy the cards, they belong to you - how do you feel about the seller treating *your* cards poorly?

I guess the platsic boxes he is talking about are much smaller than a starter box, more like a business card holder.

Yes, the plastic boxes I'm talking about are designed for trading cards. Ultra Pro has some two-piece boxes (not the hinged ones, those are horrible) that are very shallow and will hold 20 cards with minimal movement inside the box.

Sometimes I'll wrap the cards in plastic wrap before putting them into the box, the stickiness of the plastic keeps them from moving around at all inside the box.