The IW371665 comes from IWC's Portugieser Chronograph 41 family: a 41mm case, a twin-register dial with chrono minutes at 12 and running seconds at 6, feuille hands, and the in-house calibre 69355 behind the sapphire back. A fake IW371665 gets the outline right almost every time and the small stuff right maybe half the time. If you know which five or six details to look at, you can sort a $150 junker from a $700 replica in about a minute.
What the real reference gives you
The Portugieser Chronograph 41 wears wide and thin, with long slender lugs, a domed crystal, and a dial that is mostly empty space. That emptiness is the hard part for a replica maker. On the real watch, the two subdials sit on a clean vertical axis with generous margins to the case edge, the rail track is fine and even, and the applied numerals are polished on their top faces. Copy the layout badly and the whole dial reads as cramped, even in a photo.
Where replicas split into tiers
Under $200
Usually a quartz or low-grade automatic inside, thicker case, printed indices instead of applied, and a date wheel with the wrong font. Fine if you want the look for a weekend. Not fine if anyone gets within arm's length.
$250 to $450
This is the mid tier. Asian 7750-based chronograph, applied markers, decent sapphire. Flaws tend to show up in hand shape, pusher length, and the caseback engraving, which is often shallow and off-center.
$500 and up
The tier people call super clone. Case dimensions land within a few tenths of a millimeter of the genuine, the dial printing is crisp, and the movement is either a decorated 7750 or a closer copy of the 69355 layout. At this level the question stops being "is it obvious" and becomes "is it worth servicing."
The checks that expose a bad one
- Dial printing. Look at the IWC wordmark and the Schaffhausen line. Blurry edges or a font that looks slightly wide are a tell.
- Subdial spacing. The 12 and 6 registers should sit symmetric on a vertical line, with equal air above and below.
- Case thickness. Genuine is about 13mm. Anything noticeably fatter means a cheap movement stuffed into a thin case.
- Pushers and crown. They should be the same finish as the case and sit flush, not proud and shiny.
- Caseback. Inscription depth and font matter more than the movement decoration you can barely see.
- Crystal. Anti-reflective coating should cut glare without the blue haze that cheap sapphire gives off.
The movement question you should ask
Ask the seller to name the movement and send a photo with the caseback off. Most replicas run a modified Asian 7750, which gives you the right subdial layout but a thicker stack and a 40-hour-ish reserve. A few run a closer copy of the 69355, an in-house IWC design with a 46-hour reserve. If the seller dodges the question, assume the worst tier. Also ask who services it, because a chronograph with a rough module is a paperweight six months in.
Price bands and what they buy
Roughly: $120 to $180 buys a quartz or entry automatic, $250 to $450 buys a wearable automatic with visible flaws up close, $500 to $800 buys the top replica tier, and anything over $900 for a fake is a seller betting you will not compare prices. Genuine IW371665 pricing sits in a completely different world, which is exactly why the replica market exists for this reference.
Bottom line
Judge a fake IW371665 on the dial first, the case profile second, and the movement third. If the dial is right and the thickness is close, most people will never know. If the dial is wrong, nothing else saves it.