Even if you could leave feedback it probably won't help if the seller isn't selling anything anymore. If you paid via Paypal and the transaction is less than 45 days old, you can open a dispute with Paypal. Some people who bought hacked players were able to get their money back. However, if your seller has closed his Paypal account too then you may be out of luck.
People in China seem to be able to have multiple seller accounts on ebay because I often see different sellers with identical information on their item description. This makes the feedback rating useless because bad sellers will just change their identity and start over again.
Good luck.
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