Short answer: fakes of the IW545105 exist, but this is not one of the IWC references that replica factories chase hardest. The number points to a hand-wound Portugieser: round case, thin bezel, small seconds, applied numerals, leaf hands, leather strap, exhibition back. Copying effort goes where the volume is, and that means the Portugieser chronographs and the Pilot line. A hand-wound dress watch with a display back is harder to fake well and easier to check. That works in your favor.

The tells are not on the front of the watch. Case shape and dial layout are the cheapest things to copy. The movement, the printing, and the caseback engraving are where fakes fall apart. Work in that order.

Start with the movement

Ask for a clear photo of the movement through the caseback, or have a watchmaker open it. A genuine hand-wound Portugieser carries decoration that costs money: Geneva stripes with real depth and clean edges, blued screws, polished screw heads, beveled bridges, and engraving cut into the metal rather than printed on top of it. Fakes show flat, glossy bridges with stripes that look like a decal, or a winding rotor where a hand-wound watch should have none.

Then test the power reserve. This family of movements is built around a long reserve, and a generic clone cannot imitate that. Wind it fully, set the time, lay it face up, and leave it alone for several days. If it stops inside a day or two, the movement is not what the seller claims.

Check the dial under a loupe

• Printing: "IWC" and "SCHAFFHAUSEN" should be sharp, evenly spaced, and level with the dial. On fakes the letters run together or sit crooked.
• Applied numerals: polished on the top face, matte on the sides, crisp edges, no glue haze underneath.
• Leaf hands: tapered and polished, no burrs at the tips, and the minute hand should reach the minute track without overshooting it.
• Small seconds: the subdial should read as a recessed, separate zone, not a printed circle.
• Dial variant: compare the listing against IWC's own reference data. Fakers mix dial and case combinations from different references all the time.

Read the caseback engraving

Reference, serial number, and material markings are engraved, not etched thin. Look at the depth of the cut and how crisp the letterforms are. Then check that the serial on the caseback matches the warranty card or papers, and that the reference matches what was advertised. A mismatched serial is the most common giveaway on an otherwise decent fake, and it is also the signature of a frankenwatch built from mixed parts.

Price and paperwork

If the asking price is a small fraction of what the same reference brings on the major marketplaces, stop there. Nobody sells a real Portugieser at a 90 percent discount, and the "inherited it, no papers, need it gone this week" story is old. A full set means box, booklet, and a stamped or digitally registered card, with serial numbers that tie together. Buy from a seller who accepts returns and allows an independent watchmaker to open the watch before the return window closes. If they refuse, you already have your answer.

Frankenwatches are the harder problem

A straight fake is easy to reject. A frankenwatch is a real case with a fake dial, or a real dial on a generic movement. Those pass a visual check and fail at the service bench. That is why a verification fee at IWC or an accredited watchmaker is worth paying before serious money changes hands. Send the watch in, or take it to an authorized dealer and ask them to verify the reference and serial against the brand's records.

The bottom line

Assume nothing from photos. Confirm the movement, the engraving, and the serial chain, and have the watch opened by someone with no stake in the sale. On this reference the front of the watch will usually look right. The back is where the truth sits.