Keep an eye on it, I am doubtful of the dealer's diagnosis. First of all, the tank is usually only 2-3 gallon full coming out of the factory, so most of the gas during delivery is not French gas. Second, if it is bad gas from the factory, it would have been affecting a whole batch of their new delivery across the country and this should be a well known issue, and it should not have taken a week to figure out the problem (unless you are the first guy to report the issue).
So I suspect it is something else, the 4 key reasons raised by Jeepster55 could be the real cause. It seems like smart has a much lower tolerance than most other cars if that is the case. It is not a bad thing per se, but it does create headache for people living far from the dealers, or if the dealer does not offer loaners for a multi-day repair.
At least it is nice to hear it is over for you now.