The short answer: before you judge a watch advertised as "IW938243," confirm that the reference exists. IWC issues reference numbers in a fixed pattern, and a number the brand does not list is the strongest single signal that you are looking at a counterfeit, a franken-watch, or a listing built from copied text. That check takes two minutes and it does more work than any side-by-side photo comparison. The criteria below run in the order that saves the most time: reference validity, caseback engraving, dial furniture, movement, paperwork, and price.

1. Check the reference number before anything else

A reference number should resolve to a model family, a case size, and a production era. If a seller quotes IW938243 and cannot name the family it belongs to, or the number on the guarantee card does not match the number engraved between the lugs, stop there. Genuine references repeat in the same form in three places: caseback, card, and the brand's own records.

• Pro: Costs nothing and needs no tools.
• Pro: Catches the most common failure, which is a real watch sold under an invented reference.
• Con: Vintage and market-specific references can be missing from public lists.
• Con: A valid reference proves the number is real, not that the watch is.

Use this step when: all you have is a listing and a photo, which is most of the time.

2. Read the caseback engraving

Counterfeiters get the layout close and the depth wrong. Genuine engraving is cut into the metal with crisp edges and even depth. Printed or laser-etched fakes look shallow and blur at the edges under a loupe. Reference, case number, and material should sit in expected positions with even spacing, and the font weight should match known examples of the same era.

• Pro: Decisive on macro photos, and sellers rarely fake the macro shot well.
• Con: Polished or serviced casebacks lose definition, so age can look like fraud.

Use this step when: the watch is in hand or the seller can supply a high-resolution close-up.

3. Compare dial furniture and hands

Applied markers sit flat, with no gaps under the feet. Printing on a genuine dial sits on top of the lacquer with clean boundaries. A reprinted dial shows ink bleeding into the surface and markers that do not align with the minute track. Hands should be the right length and shape for the reference, and finished on the underside as well as the top, which is where cheap assemblies give themselves away.

• Pro: Visible without opening the watch.
• Con: Aftermarket replacement parts confuse the picture, since a genuine watch can carry a non-original dial.

Use this step when: you are comparing a candidate against catalog photos of the reference.

4. Let the movement decide the argument

With the caseback off, movement finish is the hardest thing to copy at a low price. Look for consistent perlage or Geneva stripes, polished screw heads with clean slots, correct rotor engraving, and a balance that swings without wobble. A quartz movement inside a watch sold as an automatic IWC ends the discussion on its own.

• Pro: The single most reliable authenticity signal.
• Con: Opening a watch voids most warranties and needs a watchmaker.

Use this step when: the amount at stake justifies a watchmaker's inspection fee.

5. Weigh the paperwork and the price

Cards, booklets, and boxes are copied well, so treat them as supporting evidence rather than proof. Price is the louder signal. A figure far under the market for that reference is not a bargain, it is a warning. Ask for service history and for the name of the dealer who supplied the watch, then check whether that story holds together.

• Pro: Paperwork and price history are easy to ask about in writing.
• Con: Genuine watches are sold without boxes every day, so a missing box alone proves nothing.

Use this step when: you have narrowed the field and need a final filter before paying.

6. If you want a replica, buy it as a replica

A replica bought as a replica is one transaction. A replica sold as genuine IW938243 is fraud, and the two should never be confused. Honest replica sellers name the movement, give the case diameter and thickness, show their own photos, and state the watch is a replica in the listing. Anyone who claims a reference the brand does not publish, or who refuses a movement photo, is not selling you a replica. They are selling you a story.

Recommendation: if you want the look at a fraction of the cost and accept the trade-offs, buy from a seller who labels the watch as a replica and states the movement and dimensions. If you believe you are buying a genuine IWC, run steps one through six in order before any money moves, and treat a reference you cannot verify as a stop sign rather than a detail.