Ebay & Amazon take a nice chunk of change. Then you throw in the credit card processor, whether it is PayPal, Google Wallet, or some other merchant solution, they take their cut, at least with Ebay. It's one thing if it is a small item that doesn't get hit too heavy, but talking about $479-$609, that's some fees lost. Then you have the emulator police trolling Ebay, except for the guy who is selling SD cards full of copyright material geared towards the Pandora (though I haven't looked for this scam lately).
For the occasional people who sell used Pandora on Ebay, that right there is good enough promotion for the site. Anyone looking through Ebay, finds a used Pandora can do a web search and find my shop or ED's shop pretty quick for a new unit.
Knowing that Amazon sides with the buyer vs the seller also makes this risky. Easy scam right there for a free Pandora.