First of all let me say that I admire Shadowpanther's passion on the subject and trying to enact change but I think he's going about it the wrong way.
Regarding a few points that were made:
The people that are selling on ebay as a business are the people that should be charging for their time. If it's their primary business then their time is certainly valuable to them and they should be compensated for it.
Also, maybe they are trying to market their business using their boxes/tape etc similar to how BBTS or Amazon does with their business. Then using USPS boxes don't fit their needs. And even if they aren't marketing their business priority mail and even fed ex packaging doesn't fit everything. And a lot of people do just buy boxes because they don't want spend their time searching for a free box that will work.
As for the guy that was charging $13 for mailing that toy. Yes you and the seller may be on the coast but have you ever thought about what it will cost him to ship the toy across the country. At that point, depending on the weight of the package, $13 is a crazy amount. He's decided to take the guess work out of shipping for himself and just said I'm charging $13 for it.
Finally, by you clicking on that button to buy the item from the seller you are already agreeing to their terms and prices. As long as the seller isn't being deceitful in their listing and how much you will be paying in shipping then there's really nothing ebay or paypal is going to do to help. It's your choice whether or not to buy something. I run into a lot of people lately that don't understand the idea of a contract. From a legal standpoint, they made an offer you accepted it. You pay and he ships. If you short pay then obviously he's not going to send the merchandise. If he ships it without packing material or he takes longer than promised then those are things worth complaining about. When you go into a purchase knowing that the seller is charging you $10 but you know it's only going to cost him $6, that's your choice. Don't blindside the guy after the fact because he charged you $4 more than it actually cost him. I'm pretty sure somewhere on ebay it says that buying or bidding is creating an agreement between you and the seller.
If you don't like his price then ask him a question and see if he'll work with you.
After reading your post, I'm scared to sell on ebay.