Short answer
The reference IW329108 sits in IWC's Aquatimer Automatic 42 line: steel case, roughly 42 mm, 300 m water resistance, a rotating dive bezel, and IWC caliber 30120 inside. A fake IW329108 is either a counterfeit being sold as genuine or a replica built to resemble one. Three checks settle the question faster than anything else: the movement and its finishing, the caseback engraving, and the way the bezel and crown actually operate. Dial print and paperwork are confirmation, not proof.
This reference gets faked far less often than a Submariner, which cuts two ways. You are less likely to meet a copy, but the copies that exist circulate precisely because few buyers have held the real watch.
Start with the movement
Aquatimer Automatics run IWC caliber 30120, a Sellita-based automatic with a 42-hour reserve and a 4 Hz beat. You cannot judge it from the outside, so budget for a watchmaker to open the back. Genuine finishing is even: crisp engraving on the rotor, consistent brushing, no tool marks around the screws. Copies at this price point tend to hide a Seagull or Miyota base under a rotor stamped with IWC text, and the stamping is the giveaway. Letters look blurry, spacing drifts, and the surface under the rotor is left unfinished.
One quick screen: this model normally carries a solid, engraved caseback. A listing that shows a sapphire display back on a 329108 is showing you a problem, not a feature.
Caseback and engraving
IWC engraves deep. Run a fingernail across the reference number, the serial, and the water resistance text. Genuine engraving has walls you can feel and sharp terminal points on every digit. Counterfeits are usually laser etched, so the edges are soft and the depth is shallow. Check that the reference on the back matches the reference on the paperwork and the case number inside the lugs, where IWC stamps it. Mismatched numbers turn up often on assembled fakes.
Bezel, crown, and hand feel
Turn the bezel through a full rotation. On a genuine Aquatimer the action is firm, indexed, and free of side-to-side play. Copies feel gritty, or loose enough to shift when you bump the watch. The crown should unscrew smoothly, thread cleanly, and seat with a positive stop. Cross-threading and a spongy stem are two of the most frequent flaws on replicas of this case shape.
Dial, lume, and crystal
Applied markers should sit flat and level, with lume filled flush to the frame. On copies the fill is often domed, uneven, or spilling over the edge. Look at the print under magnification: the spacing between the IWC mark and the model text, the weight of the strokes, and the date font in the window. IWC uses anti-reflective coating on both faces of the sapphire. Cheap coating shows up as a milky sheen at an angle, and the crystal scratches more easily than it should.
Bracelet, clasp, and weight
End links should meet the case with no gap and no rattle. The clasp should close with a solid snap and no side play, and the finishing inside the clasp should match the outside. Weight is a weaker tell than people assume, since most replicas use steel too. Judge the machining, not the mass.
Price and paperwork
A price far below the pre-owned market is the loudest single signal. So is a seller who cannot produce a receipt, a service record, or a serial that matches. If you want certainty, send the watch to an IWC service center for a service estimate. They will refuse to service a counterfeit, and that answer is worth more than any forum opinion. In the US, selling counterfeit goods is illegal and customs can seize imports, so a deal that looks too good usually carries more risk than the discount covers.
Where replicas of this reference fall short
- Bezel coupling with play, or a bezel that turns both directions.
- Shallow caseback engraving and soft fonts.
- Lume fill that is domed or uneven at the edges.
- A decorated rotor over a base movement that is not a 30120.
- Crown threads that catch or strip.
- Weak or single-sided anti-reflective coating.
Bottom line
Buy the seller as much as the watch. A genuine IW329108 with a traceable history, correct engraving, and smooth controls is not hard to verify once you know where to look. A copy fails on the inside, and the inside is the part you cannot see in a photo. Pay for an inspection before you pay for the watch.