Cartridge without serial?

Cartridges have serial numbers? Huh. Did not know that. Oh, and you can't warranty anything without a serial number. Who'd a thunk? Learn something new every day.

There are a few like juki on Ebay and Kron here on Agon that sell these "gray market" cartridges. There are buyers (from the number of reviews) that would rather pay these discounted price than the full retail price (plus tax) that a dealer would otherwise charge. What is your risk level?  If something happens to cartridge during the warranty period, you will not be able to send it to the dealer, but rather to repair places like Soundsmith or VAS Audio at your own cost - the wait can be long. That's the trade-off. If its the two sellers that I mentioned above, I wouldn't be too worried about the authenticity/quality.