Short answer

Two things catch almost every fake IW545180: the six digits engraved on the caseback, and the movement you can see through the sapphire back. Photograph both, then compare them to the official IWC listing for that exact reference. If the dial matches one variant and the engraving matches another, someone built that watch from mismatched photos. You do not need to open the case to reach that conclusion.

What the reference number tells you

IWC labels its watches with IW plus six digits. In IW545180, 5451 is the base family reference and 80 is the specific case and dial variant. That last pair matters more than most buyers expect. Two watches can share a base reference, look nearly identical in a thumbnail, and still differ in dial colour, case metal, strap, or movement. Replica makers frequently copy the dial from one version and engrave the reference from another, because the two images came from different sources.

So the first step is unglamorous: pull up the full six digits in the brand's own archive, write down the dial colour, case material, strap type and movement family, then check those four things against the watch in front of you.

Checks that catch most fakes

Caseback engraving

Genuine engraving is crisp and fairly shallow, with sharp edges and even spacing between the reference, the case number and the material marking. Fakes usually read deeper and softer, and the font weight drifts from line to line. Run a fingernail across it. Real engraving feels like a fine scratch. Cheap engraving feels like a trench.

The movement behind the glass

If the reference is a hand-wound model, there should be no rotor at all. On an automatic, the winding mechanism should look like it belongs to the watch, not like a decorated plate bolted over a generic movement. Look for stripes that stop cleanly at a plate edge rather than running off into nothing, screws that are genuinely heat-blued instead of painted, and bridge engraving that is legible under a loupe.

Dial printing and markers

Applied numerals sit proud of the dial with polished bevels that catch light from two directions. Printed text and the rail track should stay razor sharp at 10x magnification. Replicas tend to show slightly fat lettering, a rail track that fades at the edges, or markers that sit a fraction too low.

Crown, lugs and case finishing

Real case work has crisp transitions where brushed surfaces meet polished flanks. The crown should thread smoothly and the logo should be cut, not cast with rounded edges. Fakes often feel grainy when you wind or set them.

Weight and strap

A steel case around a proper movement feels dense for its size. On the strap, genuine alligator has an irregular scale pattern that changes across the length. Embossed leather looks stamped and repeats.

Where even good replicas slip

The top tier of the replica market is genuinely close, and anyone selling "1:1" is describing their best attempt, not an identical object. The giveaways are small: a subdial a hair too small, a date font that is one weight off, a crown that spins with grit, lume that fades in twenty minutes. Buy the seller's willingness to show detail, not the phrase on the listing.

Questions worth asking

• Can you send a straight-on, in-focus photo of the caseback?
• Can you photograph the movement with light angled across it, not straight on?
• Is there a recent timing reading or service record?
• What happens if my watchmaker opens it and disagrees with you?

Bottom line

Verify the six digits, verify the movement, then verify the small stuff. If a seller dodges any of those three, the watch is not the problem. The seller is.