Short answer
A "replica Cartier Ruban 31mm" is a counterfeit. It is a watch built by an unaffiliated factory that copies a Cartier design and stamps the Cartier name on the dial, caseback, and clasp. It is not a factory second, not an overrun, and not a grey-market Cartier. In the US it is an infringing product, and the practical downsides, no warranty, no spare parts, no resale value, and a real chance of seizure at the border, usually outweigh whatever the listing saves you.
What the Cartier Ruban actually is
Ruban is one of Cartier's quieter jewelry-first lines, built around a ribbon-like case and bracelet motif rather than a sport or complication story. Pieces in that family skew small and dressy, and 31mm sits in the ladies' dress-watch range. Here is the part most listings skip: Cartier does not publish a 31mm Ruban spec sheet that a replica maker could copy from. When a seller leans hard on an exact millimeter figure, that number usually came from a listing template, not from a caliper on the actual watch.
Why the spec-heavy listings are a warning sign
- Case measurements vary from batch to batch, so the size you read is rarely the size you get.
- Photos are often of a different unit than the one shipped, sometimes of a genuine watch.
- "Swiss movement" and "sapphire crystal" get used loosely, and nobody downstream can verify the claim.
- Warranty language is invented by the seller, since no manufacturer stands behind the piece.
The legal side, briefly
Trademark counterfeiting is a federal crime in the US under 18 U.S.C. 2320, and it is also actionable in civil court under the Lanham Act. Customs and Border Protection can seize counterfeit goods at the border and destroy them. When that happens, you lose the watch and the money you paid, and repeat importers can face fines of their own. This is not a theoretical risk. Small parcels get pulled regularly.
What you actually receive
Plating that thins and discolors within months. Movements that are unmarked clones with no service documentation. Cases that do not match the bracelet's finish. And a servicing dead end: Cartier will not touch a counterfeit, and most independent watchmakers decline them too, because there are no parts to order. A $200 repair estimate becomes a $200 problem with no fix.
If you love the look
Buy the real thing pre-owned from a dealer who provides papers and a service history, or put the same budget into a small jewelry-house watch with a ribbon-style case. You get something that keeps working, keeps its value, and does not arrive with a customs letter.