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Jeff SOne buyer of high-grade 1950s material to whom I have sold cards a couple of times has another solution (albeit not as airtight as Adam's). Each time I sold something to him, he included a message saying something like, "Please ship cards in a padded envelope with proper protection. No crummy team bags, please." It's easy enough to do, especially if you're only worried about a small percent of transactions. At the very least, it'll let the seller know that you're paying attention and expect that the USPS won't have a chance to damage your item.