The Short Answer
There is no Cartier reference 4307. When a listing reads "fake Cartier Rotonde 4307," the number almost always comes from the 430 MC, the thin manual-wind caliber Cartier uses in the Rotonde de Cartier line, or it is a seller's own stock code dressed up to look official. So the string mixes a model family, a movement, and a made-up number to catch search traffic. First question for any seller: which of those three are you actually showing me?
The Rotonde de Cartier, Without the Hype
Cartier introduced the Rotonde as a round, classically proportioned dress watch, which set it apart from the Tank and Santos shapes. Most executions land between 40 and 42 mm. Steel, pink gold, and white gold all appear in the catalog, and the line has carried everything from a plain small-seconds dial to the Astrotourbillon and the Mystery watches.
- Round case, slim lugs, sapphire crystal front and back on most references
- Caliber 430 MC: manual wind, about 2.1 mm thick, small seconds on some variants
- Guilloché or flinqué dials on the classic pieces, floating elements on the showpieces
- Alligator strap with a gold deployant clasp on the gold models
Where the Copies Give Themselves Away
The 430 MC is a genuinely thin movement, and that is hard to fake cheaply. Most replicas hide a stock automatic or a quartz module behind a solid or lightly engraved caseback, which is why the case often runs a millimeter or two thick. I look at three things first: the crown cabochon, the dial printing, and the caseback engraving. Cartier's cabochon sits flush and is a real synthetic spinel. The printed "Cartier" on a gen dial is crisp at the serifs, not soft at the edges. Engraved reference and serial numbers are cut clean and match across the caseback and the papers.
None of that makes a copy a Cartier. It only tells you how much effort went into the imitation.
Legal and Practical Reality in the US
Counterfeit watches carrying a live trademark are seized at the border, and trafficking in them is a federal offense with civil and criminal exposure. Practically, you also get no warranty, no service from Cartier, no parts support, and near-zero resale. A watchmaker who will touch a fake movement is doing you a favor, not a service. If the seller cannot tell you what caliber is inside and where the case was made, that silence is the answer.