You’re not out of luck with eBay though. Ask the seller for a return and refund. If he doesn’t respond with, ‘Certainly, I’d be happy to take them back, under the circumstances.’ or something equally helpful, then open a case with eBay, and explain to eBay that there is no way the cameras can be made to work, because their seller does not have the original owner’s details, and thus they cannot be de-registered by Blink. Also tell eBay that this seller cannot sell these items without de-registering them, which he can’t do, making them effectively useless, so he needs to be stopped. Based on this eBay should resolve your issue.