To make full use of organisations like Que Choisir and INC and get access to their full product tests and advice services you will have to take out a subscription (abonnement). If all you want is product tests then you’re probably better off just buying their monthly magazine as and when there’s a subject that interests you. But for free advice on consumer issues the subscription is good value for money.
UFC QueChoisir: independent consumers’ association with local branches all over France. Apart from the usual product tests they also provide model letters covering basic consumer issues/disputes.
60 Millions de consommateurs (Institut National de la Consommation - INC) The national consumers’ association
INC with lots of useful links. Among other things there is a database of model letters but you need to be registered with them to access it.
This is the government site for the Direction Générale de la Concurrence, de la Consommation et de la Répression des Fraudes. They deal with unfair trading, fraud, consumer problems generally. There is an office in every department. Google DGCCRF + name of department to find out where it is.
Summary of consumer warranties in France. It also lets you open an online complaint against a trader.
Consumer rights are also detailed on the the EU website.