Short answer

I won't write a buying guide for counterfeit Omega Seamaster Planet Ocean Deep Black watches. A guide built to help someone buy a fake watch is a guide built to help someone commit trademark infringement, and in most cases wire money to an overseas seller with no recourse. That holds even when the request is framed as informational.

What I can do is explain what the real Deep Black is, what it costs to own legitimately, and what to buy instead if the ceramic-black look is what actually appeals to you.

What the real watch is

The Omega Seamaster Planet Ocean 600M "Deep Black" is a dive watch built around a black ceramic case and dial, with a GMT function on most references and a Master Chronometer movement certified by METAS. That certification is not a marketing sticker. It means the finished watch was tested as a whole watch for precision and magnetic resistance, and it is one of the reasons the legitimate article is easy to verify and the counterfeit is not.

It is sold through Omega boutiques and authorized dealers. Anything sold anywhere else is, at minimum, worth authenticating before money changes hands.

Legitimate paths to the same silhouette

Certified pre-owned

The secondary market is where most people who want a Deep Black actually end up. Pre-owned Seamaster listings are widely available on established marketplaces, and a proper listing includes serial numbers, service history, and box and papers. You pay less than boutique price and you own something with resale value.

Homage and independent designs

If the appeal is blacked-out ceramic and a dive bezel rather than the name on the dial, several legitimate brands build that aesthetic without copying another company's trademarks. Seiko's Prospex line is the standard recommendation for a rugged everyday dive watch, and it carries its own service network and resale market. There are also microbrands producing ceramic-cased divers at prices far below any genuine Seamaster.

Buy the look, not the deception

A watch you can wear without explaining it to a customs officer, a repair shop, or a buyer is worth more than one that photographs well for a month. If you want the Deep Black specifically, save toward a pre-owned example. If you want a black ceramic diver, buy one that is honestly what it says it is.