The LEDt never alters from rapidly flashing green.
... I'm beginning to suspect this is just broken.
I believe you are correct. You already attempted multiple "hard resets" without success. Read that page to verify you did it correctly. That is all you can do.
A continuous, rapidly flashing green light is not normal. Contact the seller through eBay Messaging, politely give him the bad news, and ask what he wants you do to. He ought to refund your money, all of it. Since it is unlikely anyone could fix it, it's not worth even asking you to send it back.