There is a love-hate relationship between the French people and the concept of buying/selling goods. Because quite about everything in France must be regulated by the state, the commerce cannot escape to the rule: the Mighty State tells you when to buy and sell things (period!) and all this is reinforced by some strange laws and cultural usage.
It all dates from back in 1906 when a law dictated that all the employees should have one day of pause in their work week (to help fight a terrible high mortality rate among common workers: 45% of them had a life expectancy of less than 40yo) and, even if the state is not religious anymore, the chosen day was Sunday for everyone, obviously a Christian cultural heritage. In the long tradition of pagan festivals transformed into sober Christian celebrations, the time had come to transform a religious symbol into a secular one: the "repos dominical" (=Sunday break) rose from the ashes and became a privileged moment aimed for rest and family bonding, or so the State, well... stated!
This Sunday break concept is so ingrained in the French minds that every government attempt of changing it in the past years rose waves of indignation and protest along with the complete dismissal as a ruthless capitalist of any foreigner who ever dared to argue against it (tell me about it!).
In accordance with this law, it is forbidden in France to keep shops open on Sundays, with some exceptions, that is! Which brings me back in childhood to the wise saying of my beloved French teacher: "There is an one and only rule to keep in mind when thinking about French grammar and this is: 'Every French grammar rule always has exceptions'". IMHO this can be extended without any remorse to the whole French society. Bless!
So if you own a shop you cannot force your employees to show up on Sundays: if you insist to open and want to stay legal, you must go and sell your merchandise yourself. On the other hand, if you are intelligent enough to have opened a boutique in an area marked as "zone touristique", a denomination accorded with the goodwill of your mayor, based on the tourist flow and demand, you are saved: there are no restrictions whatsoever in securing the tourists' money and no bad conscience to be had about the destroyed family life of your employees. However, because food is a capital interest in France (some call it 'obsession'...), the state allows the detail food shops to open in the morning until 1pm, thus making the Versailles Sunday farmer's market one of the most privileged destination of the Versaillers everywhere (before, after or in place of going to church).
But there's another exception to the Sunday off rule which manifests itself around holidays and it's a definite sign that they're approaching: upon request, you, the shop owner, are allowed to open on 5 Sundays of your choice in a year (regardless of your store's size, color, sex or religious beliefs). This is an occasion for everyone to display a poster at their door or trigger a marketing campaign proudly announcing: "Our shop is open the following Sundays before Christmas:..." Or Easter. Or French the Best in the Universe Day. (Okay, I made that last one up!).
But there is always a category of resistants and protesters in the French culture, making it not only the ally and protagonist of the most famous revolutions in the world, but also a nation prone to constant discussions and constant mutual pressure. The fine for keeping your store open on Sunday rises to 1500Eur per forced employee per day of illegal work and can even end in a court decision if the unions complain to the tribunals. Keeping your unions happy can be the key to success for some traditional Sunday outlaws (the most famous of them being Ikea) and the opposite can cost you a few million euro fine.
The ultimate pinnacle of this French Sunday saga was the demonstration organized by some retail employees a few years ago to ask the government for the liberalization of the stores' opening hours. The reason for this sudden burst of laissez faire is that they feared they will lose their jobs in the long run due to the increasing competition from the virtual world. The heretics found out eventually that nothing can change the unchangeable.
¡Viva la Revolución!