Short answer first: a "Breguet Classique 3880" sold as a fake is a counterfeit watch, and the listings that use that phrase seldom describe the same object twice. One page shows a time-only dress watch, another shows a moon phase, a third uses a photo lifted from a dealer archive. The reference number is doing search work, not describing a product. Treat that as your first signal.

What the reference number actually tells you

Breguet builds the Classique family around a fixed set of house codes: a thin case, a hand-guilloché dial, blued steel Breguet hands with the eccentric moon tip, and on many references a coin-edge (knurled) case band. Reference numbers inside that family map to complications, case metal, and dial variants, so one number should point to one watch. When it gets attached to four different configurations across a dozen storefronts, the sellers are not working from a real catalog entry.

If you want to know what a given reference left the factory as, ask Breguet or an authorized dealer. That is a short email and it settles more than an evening of forum threads.

Visual tells that survive a photograph

• Guilloché. Real engine-turned patterns are cut on a rose engine. Under even light the lines stay parallel and the pattern meets the chapter ring cleanly. Stamped or printed imitations look flat, and the lines wander as they curve.
• Hands. Breguet hands are blued steel, thin, and finished. Countersunk centers, no burrs, no wobble when you set the time.
• The secret signature. Breguet has long applied a hidden signature on the dial, visible only at a raking angle. Counterfeits tend to skip it or print it where it reads head-on.
• Case band. Coin-edge finishing is cut, not molded. Cheap versions show rounded, uneven ridges.
• Movement. Look through the display back. Hand-chamfered bridges, Geneva stripes that are actually striped, blued screws, an engraved rotor. A bare, shiny plate is the giveaway.
• Serial matching. The number on the caseback should match the movement, and both should be verifiable.

Why the counterfeit route costs more than it saves

Selling counterfeit goods is trademark infringement in the US, and trafficking in them can be prosecuted as a crime. Customs and Border Protection seizes counterfeit imports, so a package that stops at the border is money gone with no appeal. Then there is the practical side. No warranty, no service, no parts. A watchmaker will not take in a movement with no documentation, which means a cheap fake that stops running is a total loss rather than a repair. Card fraud and malware ride along with plenty of these storefronts too.

If you want the look

Thin dress watches with guilloché dials and Breguet-style hands exist at honest prices. Longines, Frederique Constant, Seiko Presage, Orient, and Tissot all make the shape without the legal baggage, and a used example from any of them holds some resale value. A genuine Breguet holds quite a lot. A counterfeit holds none, which is the part the listings never mention.

Verifying a real one before you pay

Buy from a dealer with a return window. Ask for the serial before the money moves, have an independent watchmaker open the case, and confirm the reference with Breguet. If a seller resists any of those steps, you already have your answer.