[quote name='csidegamer']GBA Games should go in a box unless cart only.
Bubble Envelopes work greate for GC/PS2/XBX Games.
I buy the big ones, 9x12, put the game in sideways and fold the rest over, for extra padding.
Always use Delivery Confirmation or you will get burned.[/QUOTE]
QFT. Absolutely. Especially Delivery Confirmation. It helps you from getting burned almost all of the time and allows you and the Buyer to do a bit of tracking.
Also, if you're going the USPS route, consider their small Priority Mail boxes if you're going to ship Priority. They offer enough room for a small number of console carts or a few DVD cases. The only problem is that you will want to put in something else to act as padding. Personally, as a cost-effective way, I use cumpled paper towels myself. Never had a problem in doing so and it prevented anything from shifting inside the box.