[thecatspajamas]

You don't have to ship Priority to use a box. If you're getting tracking, you're paying for a 3 ounce package regardless. On single cards, packing in a 400count box vs a bubble mailer typically makes zero difference in postage cost. Even if it goes up to the next ounce, you're talking about an extra 21 cents. All in, including buying the box vs a bubble mailer, you might be looking at a difference of 50 cents when shipping 1st Class. In most cases, not even that much. But it makes a world of difference in perception on the receiving end when your item arrives in a box vs a bubble mailer, even if you pass on the added expense to the buyer.

The problem with bubble mailers is that shippers think they have some special power to whisk the contents off to their destination in a protective cushion of air. They don't. Think of them more like a brown paper bag: good for concealing their contents, but providing very little protection beyond that. If you wouldn't feel comfortable putting the item in a paper bag, wadding it up, and shoving it into a hole slightly smaller than the item, it's probably best to beef up the packaging. On the other hand, if it's something you would normally drop in a manila envelope except that you need to be able to add tracking, then a bubble mailer might be okay. As long as you're okay with your envelope alternative getting folded in half to fit into a too-small mailbox.