The quick answer: on a fake IW371425, the lies show up first at the dial printing, the sub-dial functions and the caseback engraving. Genuine Portugieser Chronographs have a crispness to their printing that replica factories have not matched, and the two sub-dials do specific jobs that most fakes get wrong.

If the watch is already in your hand, start at the 6 o'clock sub-dial. On the real thing it is the running seconds. On plenty of fakes it is a chronograph counter, or the hand sweeps with a stutter that looks off. That one check ends the conversation more often than any loupe work.

What the IW371425 should actually be

The reference sits in the Portugieser Chronograph family. Roughly 41mm across and about 13mm thick, steel case, a mix of polished flanks and brushed surfaces, sapphire front and back, thin leaf hands, applied numerals and a railroad style minute track. Water resistance is rated to 30 metres, which is really splash protection. Inside, the modern versions run IWC's in-house calibre 69355, a column wheel chronograph with about 46 hours of power reserve and a 4Hz beat. Earlier 3714 references used a heavily reworked Valjoux base, so the movement you should see depends on the year of the watch.

Worth saying plainly: verify the exact reference against IWC's own listing before you argue about details. Sub-references within the 3714 family differ in dial colour, hands and strap, and a seller who gets those wrong is telling you something.

The checks that catch most fakes

1. Dial printing and applied markers

Look at the text under 12 with a loupe or a phone macro shot. Genuine printing sits flat, sharp and slightly raised, with clean edges on every letter. Fakes tend to look soft, or the ink bleeds a fraction at the corners. The applied numerals should sit level, with no gap under one edge and a shadow under another. On cheaper replicas, the minute track dots are unevenly spaced, and the sub-dial rings are printed thicker on one side than the other.

2. Sub-dial layout and function

Run the chronograph. Start it, watch both counters move, then reset. The reset should snap back to zero instantly and identically on both. A drifting or lazy reset points to a stock chronograph movement dropped into a case that was never designed around it. Also check which counter does what, because a fake built on a generic movement often has the functions swapped.

3. Caseback engraving and movement finish

The sapphire caseback is the best free inspection you get. Genuine engraving is deep, with crisp edges and consistent depth across the whole text. Replica engraving looks shallow and slightly rounded, like it was stamped and polished over. Through the glass, look at the rotor, the bridges and the perlage. Real IWC finishing is even and deliberate. Fakes show machining marks, wobbly circular graining and screws that do not sit flush.

4. Pushers, crown and the winding feel

Genuine chronograph pushers have a defined, mechanical start and a clean return. Fakes usually feel spongy or gritty, and the reset pusher can have noticeable travel before anything happens. Winding the crown should feel smooth with a light resistance. If it grinds, or the crown wobbles in the tube, walk away.

5. Strap, buckle and hardware

Strap quality is where replica makers economise hardest. Genuine alligator has a natural scale pattern that changes across the strap. Fake embossed leather repeats. The buckle engraving should match the caseback in depth and font, and the pin should be polished and centred. Spring bar fit matters too. A loose fit that rattles against the lugs is a bad sign on a watch at this level.

Why the movement is the hardest thing to copy

The 69355 is a column wheel design with a vertical clutch arrangement, and the pusher feel comes from that architecture. Replica makers can clone the look of a movement, and some do it well enough to fool a photo. What they struggle with is the feel and the long term consistency. A cloned chronograph module often shows weak amplitude after a year, and the chronograph seconds hand develops a slight wobble. Ask for a timegrapher reading if you are buying remotely. Refusal is an answer.

Price reality check

Genuine IW3714 references trade on the secondary market in the mid four figures to low five figures depending on age and condition. Replicas sell for a few hundred dollars. Anything in between, say a "great deal" at a third of market price, is either a fake sold as real or a stolen watch. There is no third option that ends well for the buyer.

If you only get one check

Get a clear macro photo of the dial text and a photo of the caseback with the movement visible. Those two images settle most questions in under a minute. Buy the seller as much as the watch, and prefer dealings where the watch can be inspected or returned.