Short answer

IW545178 is not a reference number IWC writes that way. The brand uses IW followed by digits, and catalogs split the family and series with a hyphen, so a Portuguese reference turns up as something like IW5454-08. When a listing prints one unbroken run of digits, shows no movement photo, and describes the dial in vague terms, you are looking at either a mislabeled watch or a replica with a number invented to look official. Both are common on classifieds and social media sales. Neither is worth genuine money.

What a real IWC reference looks like

Pull up the model on IWC's own site or in an auction archive before you message a seller. A correct reference maps to one case size, one dial variant, one movement, and one production window. If the seller's photos show a different bezel, a different subdial layout, or a caseback with the wrong engraving, the number does not matter. The watch is already wrong.

Where replicas give themselves away

I look at four things in order, because each one is harder to fake than the last.

• Dial printing. Genuine IWC text is crisp at 10x. Replica printing looks slightly soft or thick, and the subdial rings often sit a hair off center.
• Case finishing. Run a fingernail along the lug edges. Real brushing and polishing meet in a defined line. Cheap replicas blur the transition or leave a rounded edge.
• Crown and pushers. Threads should feel tight and consistent. A gritty crown with visible machining marks is a strong signal.
• Caseback engraving. Reference, serial, and material stamps are shallow on most fakes, with uneven depth across the characters.

The movement is the tell you cannot fake cheaply

Ask for a clear photo of the movement through the caseback or a video with the watch running. Genuine in-house calibers show specific bridges, jewel counts, and finishing patterns that match the reference. Most replicas hide a generic automatic under a decorated plate. If the seller refuses a movement shot, stop there. No honest seller of a four-figure watch refuses that request.

Papers, boxes, and serial numbers

A card with a matching serial is a starting point, not proof. Replica sellers print cards too. Cross-check the serial against the caseback stamp and the movement number where visible. Also check the sale price. If a watch that trades used in the high four figures is offered near a tenth of that, the number on the listing is the least of your problems.

Before you send money

Buy the seller as much as the watch. Established platforms with buyer protection cost more and are worth it on this tier. If you want a replica, buy it knowing it is a replica and pay replica money. Do not pay genuine money for a watch whose reference number does not exist.