I've travelled twice in the last year from Basel to Luxembourg and Brussels (on the direct train that starts in Zurich). Both times French customs boarded at Basel, checked all passports and questioned in quite an intimidating manner anyone with a non-French passport - where are you going, where do you live, what is the purpose of your visit, do you have anything illegal in your luggage (!!), etc. On the most recent trip, a poor man sitting near me (Scottish, I think) had his suitcase searched and was then hauled off, never to be seen again, for having a large amount of euros in his possession.