Do You ever see a watch online or at one of the discount stores, then see the exact same thing at a jewelry store for 2 to 3 times more? Ever wonder why?
A black market watch is a stolen, counterfeit or fake watch.
Gray market watches are genuine, authentic products that are sold through an unauthorized source. Here's how it works: Watch brands sell watches primarily via Authorized Dealers who sign agreements with the brands to only sell in the store at certain prices and to continue buying watches regardless of how well they move their inventory. This can leave the Authorized Dealer with surplus inventory. They need to offload it somewhere–so they sell it to grey market dealers who turn around and flip the watches online at deep discounts.
So, what's the down side to this? There is no factory authorized warranty. Generally, the selling company will provide an inhouse warranty of their own, but they won't have access to original parts and, generally, any work they will offer to have done will be inferior. Basically, you can plan on the warranty being worthless. Additionally, these watches rarely will have a serial number, as the manufacturer could use this to trace which Authorized Dealer sold the watch. This lack of serial number will preclude the watch from being repaired at any authorized repair center. In other words, you probably won't have access to parts.
Here's an interesting article concerning the "gray market" from a 2015 court case between Costco andand Omega, a subsidiary of the Swatch Group: