Answer first

IW371758 is an IWC reference number. IWC uses the IW3717xx block for Portugieser chronograph models. A fake IW371758 is a counterfeit watch built to look like that reference. It copies the dial layout, the case shape, and the caseback text. It does not hold an IWC movement. IWC records are the source that confirms case metal, dial color, and movement for a given number. Verify the number there before you pay.

Step 1: Check the reference against IWC records

IWC publishes reference numbers, case sizes, and movement types. Match the seller's number to that data. A frequent error on counterfeit watches is a reference number that does not match the dial layout in the listing photo. If the number and the photo disagree, stop.

Step 2: Read the caseback

IWC engraves the reference and a serial number on the caseback. Check the font, the spacing, and the depth of the cut. Laser etching on a counterfeit looks shallow and flat. Genuine engraving has crisp edges. Match the serial to the movement number. A mismatch between caseback serial and movement serial is a red flag.

Some sellers show a stock photo of a genuine watch and ship a different item. Ask for photos of the actual caseback with the serial visible.

Step 3: Inspect the dial and subdials

  • Print quality. Applied numerals and the IWC logo sit level. Counterfeit logos sit high or crooked.
  • Subdial spacing. Two-register layout. Wrong spacing points to a generic movement.
  • Date window. Check font and alignment. Date text that differs from the rest of the dial text is a sign of a copy.
  • Hands. Check length and finish. Counterfeit hands are short or dull.
  • Chronograph pushers. Press each one. Genuine pushers have firm travel and a clean reset.

Step 4: Movement

Ask for a movement photo and a timegrapher reading. IWC chronographs use IWC calibres. A counterfeit uses a generic Chinese or Swiss clone movement. Look at rotor engraving, jewel count, and finishing. Blued screws that are painted, not heat treated, mark a copy.

Step 5: Price and market context

Counterfeit watches move through the same channels as other fake goods. The OECD tracks this trade and lists watches among the most copied product categories. A price far below market for a used IWC is the clearest single signal.

What to do

Buy from a dealer with a written return policy. Pay with a method that allows a chargeback. Get a service quote from an IWC authorized service center before the return window closes. If the watch fails, return it in writing and keep the photos.

IWC has not published a public database that maps every IW3717xx reference to every dial variant. Confirm details with IWC customer service or an authorized dealer.