Short answer: a fake IW329140 fails on three things before you ever see the movement. The outer bezel does not drive the inner dive scale, the date font is wrong and sits off-center in its window, and the caseback engraving is shallow and laser-cut instead of stamped. Check those in that order. Aquatimer Automatics in the 3291 family are common enough that clean used examples turn up often, so there is no reason to gamble on a questionable one.

What the IW329140 Is

The IW329140 belongs to the IWC Aquatimer Automatic line: a 42 mm steel case, 300 m water resistance, sapphire crystal with anti-reflective coating on both faces, and an automatic calibre from the 30120 group with roughly 42 hours of reserve. The bezel is the interesting part. The outer ring is linked to an inner scale, so turning the ring moves the dive markings under the glass. That linkage is what most replica makers skip, because it costs money to machine and almost nobody notices until they own the watch.

Check the Bezel First

Turn the outer ring. On a genuine watch the inner scale moves with it, with firm steps and almost no back-play. On a fake the outer ring spins free and the inner scale is printed on a fixed ring, so it never budges. Some replicas glue the outer ring down and dress it with fake screws. Run a fingernail along the bezel edge. Real ones sit flush and tight to the case. Replicas wobble, or sit high enough that you can see a gap underneath.

Dial, Date, and Lume

Zoom in on the dial with a phone camera at 3x. Applied indices on a real IWC are polished on the bevels and matte on top, and they line up with the printed minute track. Fakes show crooked markers, uneven lume fill, and printed text that is thicker than it should be. The date should sit centered and level in the aperture, not crowded to one side.

Lume is the fastest tell at night. Super-LumiNova on a genuine watch glows a pale blue-green and fades over hours. Cheap replica lume is patchy, dim, and often a sickly green under any light.

Case, Crystal, and Finish

IWC brushes and polishes with a clean line between the two finishes. Replicas blur that transition, or polish surfaces that should be brushed. Look at the crystal from a steep angle. Double-sided anti-reflective coating makes a real IWC nearly disappear, while replica glass throws back a blue or purple haze and mirrors your face.

Check the end links where the bracelet meets the case. On a genuine watch they sit flush with no rattle and no gap at the lugs. That gap is one of the first things to go on a replica case.

Caseback and Movement

The engraving on a real caseback is deep and crisp. Replica engraving is shallow, with rounded edges where the laser burned the metal. The reference number and serial should be stamped on the case between the lugs, not etched across the outside of the caseback.

Ask for movement photos. A 30120-family IWC shows striped finishing on the bridges, a decorated rotor with engraved branding, and blued screws. Replicas often hide the movement behind a solid caseback for a reason. When they do show it, the finishing is printed rather than machined, and the rotor lettering is filled with paint.

Price and Paperwork

If the asking price is a small fraction of what the same reference sells for on the pre-owned market, that is your answer and you can stop reading. Replicas of this reference trade for a few hundred dollars. A real one does not, and nobody who owns one is dumping it for a tenth of market value. Compare against sold listings, not asking prices, because asking prices are fiction on every platform.

Questions Worth Asking a Seller

• Can you send photos of the movement, the caseback, and the reference stamping between the lugs?
• Does the reference number on the case match the one on the paperwork?
• Has a watchmaker opened the case, and will you cover an authentication if I pay for one?
• What did you pay, and do you have the original receipt or service history?
• Will you meet at a watchmaker's bench so the case can be opened before money changes hands?

The Bottom Line

One minute with the bezel and one minute with a phone camera will settle most of this. If the inner scale does not move when the outer ring turns, walk away. If the date font is wrong or the caseback engraving looks burned rather than stamped, walk away. Everything else, including the movement, you can confirm at a bench for the price of a service estimate.