The seller lied about getting "rid of the box to save on shipping," a common lie on both ebay and Amazon Marketplace. The CPU was probably pulled from a retired PC. I bought a used CPU on Amazon Marketplace which was as clean as new, though the seller was honest and admitted that it was pulled from a Dell.
Thank you for contacting the Intel Communities.
Regarding the warranty of the products, in order to claim it, only the original owner of the device is able to do this.
Also, as you probably know, OEM processors are not covered by Intel in the warranty.
Here you can find with your location, authorized resellers from Intel that certainly will provide you with a CPU with warranty coverage.