Short answer
A fake IW329130 gives itself away at the caseback. Genuine IWC engraving is cut into the metal with even depth and sharp edges, and the reference and serial numbers tie back to the papers and the movement. Copies use shallow etching or printed film that wears off, and one number often appears across a whole batch of watches.
What you need
- A 10x loupe and a bright light
- Digital calipers and a kitchen scale with 0.1 g resolution
- Photos of the reference from the maker's own catalog
- The watch in hand, plus its box, papers, and service history
Step-by-step authentication
- Read the caseback engraving under the loupe and compare the font, spacing, and cut depth with the maker's photos of the reference.
- Measure case diameter, thickness, and lug width with calipers and match them to the published specs.
- Weigh the watch on the kitchen scale and compare it with a known genuine example on the same bracelet or strap.
- Examine the dial print at 10x, checking the brand name, line name, and depth rating for sharp edges and even letter spacing.
- Inspect the applied indices and hands for flat polishing, correct length, and clean frame edges.
- Turn the bezel through a full rotation, stop it at 12, and listen for defined clicks and correct alignment.
- Work the crown through both positions and set the date, noting grit, wobble, or a loose feel in the stem.
- Study the movement through a display back, or ask a watchmaker to open the case, then compare rotor engraving and bridge finishing with the genuine caliber.
- Check the bracelet, clasp, and spring bars for stamped markings, sharp edges, and loose tolerances.
- Compare the box, warranty card, and booklet for print quality, the right reference digits, and a serial that matches the case.
- Pressure-test the watch at a shop, because a case that fails a 100 m test does not match the rating printed on the dial.
Red flags that settle it
- Serial numbers that show up on listings for other watches
- Date print that sits low in the window or uses the wrong font
- A bezel that drifts past the marker or turns in both directions
- Lume that dims within minutes of charging
- Rotor engraving that looks like a sticker instead of metal relief
- Case screws with soft heads that round off on the first turn
- Cards or booklets with spelling errors and mismatched reference numbers
If the watch is fake
Stop the deal and ask for a refund in writing. Keep the listing, photos, chat logs, and payment records. Report the seller to the platform and to the payment provider, then take the watch to an authorized service center for a written opinion if money is already gone. A watchmaker's note carries more weight than a forum comment when a dispute is filed.