When I say auction, just to clarify I mean somewhere like Christies, Sotheby's not eBay!
We managed to pick up quite recently at Christie's London an LE Tank Basculante Millennium. It just happened to be numbered 28/365 - 28 is my birth date - so it was obviously meant for me. It wasn't going properly so we took it to the Cartier boutique who sent it back to France for a full service. They are always very happy to service, clean, repair genuine pre-loved Cartiers and when we bought my Santos, also at auction, the in-house workshop cleaned it, polished it and regulated it free, handed it back with the words "No charge - it's a Cartier!"