Short answer
Used Cartier watches get faked. The range runs from $40 quartz copies to converted pieces with a real case and the wrong movement. No single check proves a watch is real. The caseback numbers, the dial print, the movement, and the service record together give you a decision.
Check the caseback numbers first
Cartier engraves two identifiers on the caseback. The reference number is the model code, for example WSTA0028 on a steel Tank Must. The serial number is unique to that watch. Serial formats changed over time. Older pieces carry short numeric strings. Modern pieces mix letters and digits. Compare the fonts against a known photo of the same reference. Genuine engraving has even depth and clean edges. Laser etching on a fake looks shallow and grey. A serial that shows up on several listings is the most common tell.
Dial and case details
- Cartier prints its logo at a steady stroke weight. Fake dials show thick strokes or uneven letter spacing.
- Some Tank references hide the word Cartier inside the VII numeral. The mark is small and crisp on genuine dials.
- Modern dials read SWISS MADE under the 6. Older pieces read SWISS, or SWISS MADE in a different spot.
- Case thickness drifts on fakes by 1mm to 2mm against the reference spec.
- The crown cabochon is sapphire on most models. Glass or plastic is a fail.
Movement
Match the movement to the reference. A quartz Tank Must is correct. A quartz Santos is not. Cartier uses in-house calibers such as the 1847 MC and the 1904 MC, plus quartz and ETA-based movements in lower tiers. Ask for a photo of the movement through the caseback. A decorated rotor with the wrong engraving points to a swap.
Paperwork, box, and service history
Boxes and cards get copied, so a Cartier International Guarantee card proves little on its own. A Cartier service invoice with the case number on it carries more weight. Boutiques keep service records tied to the serial number. Ask the seller for the invoice.
Price and seller signals
Compare against sold listings, not asking prices. A steel Tank Must trades in a known band. A price 40% below that band, stock photos, and no photo of the caseback are risk markers. A seller who refuses a video call with the watch in hand, or who ships from a country other than the listing, is a risk.
Getting it checked
Cartier boutiques in the US do not issue written authentication letters for watches bought outside their network. They do confirm a serial when the watch arrives for service. Independent watchmakers who service Cartier can open the case and read the movement, the dial feet, and the caseback engraving. Paid authentication runs about $75 to $250. eBay Authenticity Guarantee covers watches sold at $2,000 or more in the US and routes them to a third-party authenticator first. Selling counterfeit goods is illegal in the US under 18 U.S.C. 2320 and the Lanham Act. A seller who describes the watch as a replica in writing hands you evidence.