The IW371787 belongs to IWC's Portugieser Chronograph family, the bicompax line that carries a running seconds subdial at 6 o'clock, a 30-minute chronograph counter at 12, and a date window at 3. Replicas of this reference sell from roughly $70 to $450, and nearly all of that price gap lives in three places: the dial printing, the case finishing, and the movement visible through the sapphire back. Short answer for anyone in a hurry: buy the version with a mechanical 7750-derived movement and a real sapphire crystal, and skip anything whose small seconds hand ticks.

What you are actually shopping for

IWC numbers its references in two parts. The first four digits identify the model line and the last two encode the dial, case metal, and strap combination. That matters when you compare listings, because two sellers can both say "IW371787" while showing different dials. Pull up the official product page for the reference family before you compare photos, and note the exact dial colour, hand shape, strap, and case diameter. On the Portugieser Chronograph the case is a slim round design with feuille hands, applied numerals, and a fairly thin bezel, so any replica that looks chunky in profile is already wrong.

The three tiers of fake

• Quartz junk, $50 to $100. The chronograph hand jumps instead of sweeping, the subdial at 6 ticks once a second, and the pushers feel like buttons on a calculator. Dial printing is flat and slightly blurry under a loupe.
• Mid-tier automatic, $150 to $250. Usually a Chinese 7750 clone. The sweep is smooth and the layout is correct, but movement finishing is plain, the rotor may be undecorated, and the crystal is often mineral glass or sapphire with weak anti-reflective coating.
• High-grade, $300 and up. Correct subdial spacing, sharp printing, an engraved and decorated movement, sapphire front and back, and a strap that is at least decent leather or a steel bracelet with solid end links.

Dial and crystal tells

Look at the printing under magnification. On a good replica the numerals and the minute track are crisp, the wordmark is the right weight, and the text sits at the correct distance above the 6 subdial. On cheap ones the text is heavy, the font is a touch wide, and the subdial rings are printed rather than applied. Anti-reflective coating matters more than people expect here because the dial is bright and busy; a replica with no AR coating glares and looks washed out in daylight. Ask for a photo taken outdoors at an angle, not just a studio shot straight on.

Case, crown and caseback

Case finishing is where mid-tier and high-grade versions separate. The genuine case has a mix of polished and brushed surfaces with a clean line between them, and the lugs curve down toward the wrist rather than sticking straight out. Check the crown engraving and the depth of the caseback engraving: shallow etching that reads grey rather than cut is a cheap tell. Since this reference has a display back, the movement is part of the pitch, so a plain undecorated rotor is a warning sign.

Movement questions to ask

Ask the seller three things: what movement is inside, what beat rate it runs at, and whether the subdial at 6 is running seconds or a chronograph counter. A 7750-derived automatic runs at 28,800 vibrations per hour, eight beats per second, and the seconds hand should sweep in fine increments. The chronograph should start and stop with a firm push and reset to zero instantly. If the seller cannot name the movement, that answers the question.

Buying without getting burned

Buy from someone who shows the actual watch, not stock photos, and who offers a return window. Ask for a short video with the chronograph running, the date flipping, and the watch sitting on a scale so you can compare weight to the published spec. Keep in mind that this is a replica, not an IWC, and a seller who implies otherwise is the one to walk away from. Legal treatment of counterfeit watches varies by country and customs can seize a shipment, so factor that risk into what you are willing to pay.