The quick answer
Most fake Omega Seamaster 300 and Seamaster Diver 300M watches fail the same four checks: dial printing and lume, bezel action and alignment, caseback engraving and serial numbers, and the movement under the caseback. The first three take about a minute each and need no tools. The movement check takes a watchmaker and a caseback wrench. Price is the fastest filter of all. A genuine Seamaster 300 starts near $6,000 from an authorized dealer, so a "new" one selling for a few hundred dollars is counterfeit every time.
Dial and hands
The heritage Seamaster 300 uses a sandwich dial, with lume sitting in recessed cutouts under a top plate. Fakes often print the lume instead of filling it, so the numerals look flat and slightly thick at the edges. The 2018 and later Diver 300M has a laser-engraved ceramic wave dial. On counterfeits the waves are printed on a lacquer base and reflect light as a flat sheet rather than catching it in ridges.
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Look at the text next at 10x magnification. "Seamaster" and "Co-Axial Master Chronometer" should be razor sharp with even letter spacing. Replica printing blurs, sits high on the dial, or drifts off center. The hands should have polished beveled edges that flash as you tilt the watch. Fakes show rough or matte edges.
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Lume is the giveaway I check last because it takes a few hours to judge. Genuine Super-LumiNova glows bright and fades at a steady rate. Counterfeits glow patchy, dim fast, and the bezel pip usually sits proud or slightly off center.
Bezel and case
- Genuine Diver 300M bezels click 120 times with no backplay. Many fakes have 60 clicks, a mushy action, or play that lets the triangle drift past 12.
- The helium escape valve at 10 o'clock works on the real Diver 300M. On fakes it is usually a solid cap or a glued-in cosmetic part. The heritage Seamaster 300 has no valve at all, so a valve on that model is an instant tell.
- Crowns are signed with the Omega symbol and thread in smoothly. Fake crowns have shallow etching and gritty threads.
- Case finishing on a real watch has crisp transitions between brushed and polished surfaces. Fakes show rounded lug edges and uneven brushing.
Caseback, serials, and paperwork
The Diver 300M has a solid caseback with a laser-engraved seahorse medallion and "Seamaster Professional" text. Counterfeit medallions look stamped, shallow, or shifted off the center line. The heritage Seamaster 300 has a wave-edged sapphire caseback that shows the movement, which makes the next check easy.
Serial numbers should match in three places: the caseback, the lug at 7 o'clock, and the pictograms card. Replica serials repeat across batches, and the same number turns up in forum threads again and again. A genuine watch ships with a Master Chronometer certification card, a pictograms card, and a warranty that can be activated through Omega. Fakes come with generic cards that no boutique will honor.
Crystal coating is another quiet tell. Genuine sapphire has anti-reflective treatment on both sides, so the glass nearly vanishes at an angle. Fakes usually coat only the outside and throw a blue or purple tint.
Movement
The heritage Seamaster 300 runs calibre 8912. The Diver 300M runs calibre 8800. Both are METAS Master Chronometer certified, rated to 15,000 gauss, and built with a co-axial escapement, a free-sprung balance, and a silicon hairspring. The rotor carries Geneva stripes and an engraved Omega logo with the calibre number.
Fakes almost never reproduce that package. Most run a decorated ETA or Seagull clone with a stamped rotor, and some hide a quartz movement behind a solid caseback. If a seller will not let a watchmaker open the case, walk away. That refusal is your answer.
Before you buy
- Compare the asking price with current retail. Deep discounts on a current reference are a red flag.
- Ask for the serial and reference number, then confirm both with Omega or a boutique.
- Tilt the dial under a lamp and study the wave or sandwich texture.
- Count the bezel clicks and check that the triangle lines up with 12.
- Match the caseback serial to the lug and the cards.
- Meet at a watchmaker or an authorized dealer and have the caseback opened.
One last note worth stating plainly: counterfeit watches are illegal to sell in the United States. They carry no manufacturer warranty, no service support, and no resale value. If the deal looks too good, it is not a bargain.